Automatic article feeding system

ABSTRACT

A method for feeding articles to a robot comprises the steps of temporarily storing a plurality of containers in a temporary storing device including a rest on which the plurality of containers are stacked and a separator for simultaneously separating the stacked containers from each other, stocking a plurality of containers supplied from the temporary storing device in a stocker, and feeding the stocked containers to the robot one-by-one.

This application is a continuation of divisional application Ser. No.07/968,303, filed Oct. 29, 1992, abandoned, which is a divisional ofSer. No. 668,912, filed Mar. 13, 1991, now U.S. Pat. No. 5,232,331,issued Aug. 3, 1993, which is a divisional application of Ser. No.07/227,307, filed Aug. 2, 1988, abandoned.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to an automatic article feeding apparatusfor feeding articles such as parts or units to an assembling/processingmachine, and the like and, more particularly, to an article feedingapparatus capable of feeding a necessary number of articles required bythe assembling/processing machine without delaying the feeding ofarticles.

2. Prior Art

The present applicant proposed article feeding apparatuses belonging tothe same technical field as that of the present invention in JapanesePatent Application Nos. 60-195594 (filed on Sep. 4, 1985), 61-200949(filed on Aug. 27, 1986), 61-200950 (filed on Aug. 27, 1986), and60-159610 (filed on Jul. 19, 1985). The former three out of these fourapplications were consolidated and correspond to U.S. Pat. No.4,932,828, and the last one corresponds to U.S. Pat. No. 4,844,680.

The article feeding apparatuses according to these four applications areones for feeding, to an assembling machine, articles to be assembledtherein. Each article feeding apparatus comprises a stocking means(stocker in one embodiment), adjacent to the assembling machine, capableof stocking a plurality of pallets upon feeding articles. The stockingmeant is connected to a pallet feeding means and a pallet dischargingmeans. The pallet feeding means has a function of simultaneouslyreceiving a plurality of pallets from a pallet conveying vehicle, andseparating one pallet from the plurality of pallets. The palletdischarging means has the function of discharging an empty pallet fromthe stocking means.

Each article feeding apparatus according to the previous applicationsemploys an arrangement in which the stocking means, feeding means, andpallet discharging means are arranged two-dimensionally on a singleplane. As a result, the article feeding apparatus requires a largeinstallation area, and factory layout is made complicated and difficult.

Since the feeding means and the pallet discharging means are arrangedtwo-dimensionally, different moving paths of conveying means must beprepared. The entire system of the article feeding apparatus includingthe conveying means is complicated.

Furthermore, each article feeding apparatus according to the previousapplications does not have a function of separating and drawing out anarbitrary pallet from a plurality of pallets which are fed from a feedsource and are stacked. In other words, each article feeding apparatusof the previous applications is suitable for one in which identicalarticles are fed to all the pallets and the identical articles are fedto a receiving portion.

As applications by others which belong to the same technical field asthat of the present invention, Japanese Patent Laid-Open (Kokai) Nos.60-122632 (Laid-Open date; Jul. 1, 1985), 61-206708 (Laid-Open date;Sep. 13, 1986), and 61-168452 (Laid-Open date; Jul. 30, 1986) are known.

Japanese Patent Laid-Open (Kokai) No. 60-122632 relates to an automaticparts array feeding apparatus for storing a variety of parts arrays in apredetermined container, sequentially taking out the stored partsarrays, and automatically feeding the taken-out parts array to anarbitrary position. This patent discloses the apparatus comprising astack separating unit for stacking and storing containers and separatingthese containers, a pusher for pushing out the separated containers, anintermediate holding unit for moving an empty container downward to keepa stock space for the next full container, and holding the container, alifter for stacking and discharging empty containers, and an unloadingconveyor for unloading an empty container.

Japanese Patent Laid-Open (Kokai) No. 61-206708 relates to a traytransferring apparatus for automatically transferring a tray on which alarge number of products or parts are placed in a working unit of aproduct working section in accordance with a work content so as to sendand receive products or parts. This patent discloses the apparatuscomprising a plurality of stages of stock units for loading/unloadingand supporting a tray, a transfer machine for loading/unloading the trayto/from these stock units, an elevating member for placing the trayunloaded from the stock unit thereon, a driving device for driving theelevating member, and a control unit.

Japanese Patent Laid-Open (Kokai) No. 61-168452 relates to an automaticlarge work feeding/taking-out apparatus for automatically feeding/takingout parts constituting a frame, mainly, a box-like work, of a relativelylarge work, such as a radio receiver, a radio receiver with a cassettetape recorder, a video tape recorder, a television set, or the like.This patent discloses that a rack stocking works in a plurality ofstages is transferred to the work take-out position of a robot by afeeding conveyor so that a work in each stage of the rack is taken out,and when the works in the rack are used up, the rack is sent back by atransfer conveyor and a new rack stocking works is fed to the feedingconveyor.

U.S. Pat. No. 4,651,863 U.S. Ser. No. 790,765 cited by the examiner inexamination of U.S. Ser. No. 903,412 filed by the present applicant (nowU.S. Pat. No. 4,932,828, date of patent; Mar. 24, 1988, filed on Oct.23, 1985) discloses a system for assembling electronic component kits,which relates to automated systems and more specifically to automatedsystems for constructing component kits for electronic printed circuitboards. This U.S. Ser. No. 790,765 is the continuing application of U.S.Ser. No. 528,022. The Japanese counterpart of U.S. Ser. No. 528,022 wasprovisionally published under Japanese Patent Laid-Open (Kokai) No.60-56702 (Laid-Open Date; Apr. 2, 1985). The system disclosed in U.S.Pat. No. 4,651,863 is a system for assembling component kits,comprising:

(A) a multi-level carousel means, each of said multi-levels of saidcarousel being selectively movable in at least a first direction along afirst closed path independently of any other multi-level, each level ofsaid carousel having a plurality of storage bins such that when aselected level of said carousel is rotated, a selected storage bin isselectively positioned with respect to the said first path along whichsaid carousel is rotated;

(B) first and second elevators in a fixed, horizontally spaced-apartrelation adjacent to said first path,

each elevator including a vertically movable carriage for movementbetween selected heights corresponding to selected multi-levels,

each carriage having a horizontal, rotatable turntable thereon andcarrying,

first and second retractable-extendable tray engaging means located onone and the opposite sides, respectively, of the axis of rotation ofsaid turntable and equally spaced therefrom, said tray engaging meansbeing in parallel and reversed relation to each other so that movementsof retraction and extension are in 180° opposite directions, saidrotatable turntables being operable to one and a 180° opposite positionin which said movements are perpendicular to said first path;

(C) component handling robot apparatus including a first tray receivingarea longitudinally aligned with one of said sides of one of saidturntables, and a second tray receiving area longitudinally aligned withone of said sides of the other of said turntables,

and further including a robot intermediate said first and second areasand having a working range extending thereto,

said working range further including a component collection kit areahaving kits there located to which components obtained from said firstand second areas are delivered by said robot;

(D) means controlling said carousel means, said elevator carriages andturntables, said tray engaging means and said robot, for positioning afirst selected storage bin carried by said carousel at a selectedposition and

for elevating said carriage to a position in which an empty side of saidfirst turntable is aligned with said first selected tray from whichcomponents are to be obtained, and for operating one tray engaging meansto draw said first selected tray onto said first turntable, and thenrotating said first turntable 180° and operating the other tray engagingmeans on the other side of said first turntable to place a second, atleast partly used tray in the location from which said first selectedtray was removed, and

then lower said first turntable and to align the empty side thereof withsaid first tray receiving area and drawing a third tray from said firsttray receiving area onto the previously empty side of said firstturntable, then rotating said first turntable 180° and placing saidfirst tray on said first tray receiving area,

and then repeating the operation beginning with positioning a selectedstorage bin at a selected position,

operating said second elevator carriage and turntable and associatedparts in the same sequence, but in alternating relation to the firstcarriage, and in connection with the second tray receiving area so atleast one of the first and second tray receiving areas has a traythereon at any given time,

and operating said robot to remove components from said first and secondtrays alternately and to place them in said component collection kits.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its principal object to provide an article feedingapparatus in which, when articles are fed from a feed source such as awarehouse to a section to be subjected to feeding such as an assemblingmachine, processing machine, and the like, a feeding position to thesection to be subjected to feeding is fixed, so that articles can beefficiently fed without being interrupted.

To attain the above-mentioned object, there is provided an articlefeeding apparatus which feeds articles from a feed source to a sectionto be subjected to feeding, comprising:

stocking means for stocking a plurality of containers retaining aplurality of articles in units of types of articles, the stocking meanscapable of moving one container to a predetermined position;

take-out means for taking the container moved to the predeterminedposition outside the stocking means in order to feed articles to thesection to be subjected to feeding;

temporary storing means for temporarily storing the plurality ofcontainers, upon receiving replenishment of the containers retaining thearticles from external equipment; and

replacing means for replacing a container in the stocking means with acontainer in the temporary storing means in accordance with a decreasein number of articles in the container in the stocking means to apredetermined value upon article feeding to the section to be subjectedto feeding.

It is another object of the present invention to provide an articlefeeding apparatus with good work efficiency, which can quickly replace afull container with an empty container even if a stock order ofcontainers in a stocking means is randomly set regardless of a feedingorder.

To attain the above-mentioned object, there is provided an articlefeeding apparatus which feeds articles from a feed source to a sectionto be subjected to feeding, comprising:

stocking means for stocking a plurality of containers each retaining aplurality of articles;

moving means for reciprocally moving the stocking means so that one ofthe plurality of containers is located at a predetermined position;

feeding means for feeding the articles from one container located at thepredetermined position of the stocking means to the section to besubjected to feeding;

memory means for storing a separation relationship between positions ofthe containers in the stocking means and the predetermined position; and

control means for, when one container is moved to the predeterminedposition in accordance with a predetermined moving order, reading outthe separation relationship between the position of the one containerand the predetermined position and controlling the moving means to movethe stocking means based on the separation relationship.

It is still another object of the present invention to provide anarticle feeding apparatus in which containers retaining articles arealways stocked in a stocking means, and a wait time of article feedingto a section to be subjected to feeding can be minimized.

To attain the above-mentioned object, there is provided an articlefeeding apparatus which feeds articles from a feed source to a sectionto be subjected to feeding, comprising:

stocking means for stocking a plurality of containers each retaining aplurality of articles;

draw-out means for drawing out the container from said stocking means inorder to feed articles to the section to be subjected to feeding;

discharging means for discharging an empty container with no articlesfrom the plurality of containers stocked in the stocking means; and

control means for controlling operations of the stocking means, thedraw-out means, and the discharging means,

the control means being arranged so as to complete a dischargingoperation for discharging the empty container by the discharging meanswithin a draw-out operation time of the container to the section to besubjected to feeding by the draw-out means.

It is still another object of the present invention to provide anarticle feeding apparatus in which types and numbers of articles whichare requested by a section to be subjected to feeding are prepared so asto efficiently feed articles.

To attain the above-mentioned object, there is provided an articlefeeding apparatus which feeds articles from a feed source to a sectionto be subjected to feeding, comprising:

temporary storing means for temporarily storing the plurality ofcontainers, upon receiving replenishment of containers each retaining aplurality of articles from the feed source;

separating means for separating a predetermined container from theplurality of containers stored in the temporary storing means;

stocking means for stocking the plurality of containers supplied fromthe temporary storing means so as to feed articles to the section to besubjected to feeding in accordance with a predetermined feed order;

supply means for performing a preparation operation for separation bythe separating means so as to supply a new container from the temporarystoring means to the stocking means, and a supply operation forsupplying the separated container to the stocking means;

first counter means for counting the number of articles remaining ineach of the plurality of containers in the stocking means; and

control means for causing the supply means to perform the preparationoperation for supplying a new container in place of the container whosecount value has reached a predetermined value when the count value heldin the first counter means has reached the predetermined value.

It is still another object of the present invention to provide anarticle feeding apparatus capable of minimizing a wait time in responseto a replacement request from a section to be subjected to feeding.

To attain the above-mentioned object, there is provided an articlefeeding apparatus which feeds articles from a feed source to a sectionto be subjected to feeding, comprising:

temporary storing means for temporarily storing the plurality ofcontainers, upon receiving replenishment of containers each retaining aplurality of articles from the feed source;

memory means for storing correspondences between the plurality ofcontainers in the temporary storing means and articles retained therein;

stocking means for stocking the containers supplied from the temporarystoring means in order to feed articles to the section to be subjectedto feeding in accordance with a predetermined feed order;

separating/supply means for separating a specific container from othercontainers in the temporary storing means and supplying the separatedcontainer to the stocking means; and

control means for, when the number of articles in a container isdecreased along with feeding of articles to the section to be subjectedto-feeding, searching a storage position of a container retaining thecorresponding articles in the temporary storing means based on thecorrespondence between the articles and the containers stored in thememory means, and causing the separating/supply means to separate/supplythe searched container.

It is still another object of the present invention to provide anarticle feeding apparatus which can improve installation spaceefficiency, and can reliably cope with an increase in types of articlesand number of containers.

To attain the above-mentioned object, there is provided an articlefeeding apparatus which feeds articles from a feed source to a sectionto be subjected to feeding, comprising:

temporary storing means for temporarily storing the plurality ofcontainers, upon receiving replenishment of containers each retaining aplurality of articles from the feed source,

the temporary storing means including:

a base on which the plurality of containers are stacked; and

separating means for separating a predetermined container from othercontainers of the plurality of containers stacked on the base;

stocking means for storing the containers so as to feed articles to thesection to be subjected to feeding;

signal generating means for generating a signal requesting a draw-inoperation of a predetermined container to the stocking means from theplurality of containers stacked on the base;

drive means for vertically moving the base so that the predeterminedcontainer requested by the signal generating means opposes theseparating means; and

discriminating means for discriminating whether or not the containervertically moved to the position opposing the separating means by thedrive means is a container requested by the signal generating means.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figers thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front view showing the overall arrangement of oneembodiment of an FAC system according to the present invention;

FIG. 2 is a schematic perspective view showing the overall arrangementof the FAC system shown in FIG. 1;

FIG. 3 is a perspective view showing an arrangement of a palletretaining parts;

FIG. 4 is a front view showing shapes of pallets having three differentheights;

FIG. 5 is a sectional view showing a stacked state of pallets;

FIG. 6 is a perspective view showing an arrangement of a buffer;

FIGS. 7A to 7D are front views sequentially showing a separationoperation of a predetermined pallet pa in the buffer;

FIGS. 8A to 8E are front views sequentially showing a positioncorrection operation in the separation operation of the buffer;

FIG. 9 is a perspective view showing an arrangement of an elevator;

FIG. 10 is a side view showing an elevator body in the elevator togetherwith a replacing mechanism;

FIG. 11 is a front view showing an arrangement of the replacingmechanism in a partially cutaway state of the elevator body;

FIG. 12 is a perspective view of the replacing mechanism;

FIGS. 13A to 13G are front views showing a replacement operation in theelevator;

FIG. 14 is a perspective view showing an arrangement of a stocker;

FIG. 15 is a side view showing an arrangement of a lid openingmechanism;

FIG. 16 is a side view of the lid opening mechanism in a state wherein alid is lifted up;

FIGS. 17A to 17E are views for explaining a change in movement of thestocker and the like depending on the processs order and shelf order;

FIG. 18 is a view showing an arrangement of a control unit of theembodiment, and the connection relationship between the control unit anda production management computer;

FIGS. 19A to 19C are views showing an input menu for an input device andits display state;

FIG. 20 is a view for explaining shelf position teaching of the stocker;

FIG. 21A is a view for explaining variables commonly used in controlmodules;

FIG. 21B is a view for explaining a format of queues;

FIGS. 22A and 22B are views showing vertical positional relationship ofmodule operations in the FAC system;

FIGS. 23A and 23B are flow charts of a robot control program;

FIGS. 24A and 24B are flow charts of a stocker control program;

FIG. 24C is a view for explaining a transition state of a process numberin stocker control;

FIG. 25A is a view for explaining a format of variables used in buffercontrol;

FIGS. 25B and 25C are flow charts of a buffer control program;

FIGS. 26A and 26B are flow charts of an elevator control program;

FIGS. 27A to 27G are views for explaining the pallet replacementoperation sequence using the elevator as a major component;

FIG. 28 is a view for explaining stacking of empty pallets onto anunloading mechanism;

FIG. 29 is a flow chart of a control operation for setting the system inan initial operation state;

FIG. 30 is a flow chart of a control program according to a firstmodification;

FIG. 31 is a schematic perspective view showing an arrangement of abuffer according to the first modification;

FIG. 32 is a front view showing a state wherein a maximum dispositionpitch of separation pawls in a stack separating mechanism shown in FIG.31 is set;

FIG. 33 is a front view showing a state wherein a minimum dispositionpitch of separation pawls in the stack separating mechanism shown inFIG. 31 is set;

FIG. 34 is a side view showing an arrangement of the stack separatingmechanism;

FIG. 35 is a schematic perspective view showing an arrangement of anelevator according to a second modification;

FIG. 36 is a bottom view showing an arrangement of a full palletreplacing mechanism in the elevator shown in FIG. 35;

FIG. 37 is a side view showing the arrangement of the full palletreplacing mechanism shown in FIG. 36;

FIG. 38 is a bottom view showing an arrangement of an empty palletreplacing mechanism shown in FIG. 35;

FIG. 39 is a side view showing the arrangement of the empty palletreplacing mechanism shown in FIG. 38;

FIG. 40 is a side view showing an arrangement of a replacing mechanismaccording to a third modification;

FIG. 41 is a partially cutaway front view of the replacing mechanismshown in FIG. 40;

FIGS. 42A to 42H are schematic front views sequentially showing theoperation of the third modification;

FIG. 43 is a perspective view showing a buffer comprising a liftmechanism according to a fourth modification;

FIG. 44 is a side view showing positions of sensors shown in FIG. 43;

FIG. 45 is a control flow chart of the elevator and lift mechanismaccording to the fourth modification;

FIG. 46 is a perspective view showing a schematic arrangement of anotherembodiment according to the present invention;

FIG. 47 is a perspective view showing an arrangement around a bufferbase of a buffer shown in FIG. 46;

FIG. 48 is a bottom view showing a state of the lower surface of thebuffer base shown in FIG. 47;

FIG. 49 is a side view showing an arrangement of a replacing mechanismarranged on the buffer base;

FIGS. 50A and 50B are flow charts of a control program according to theembodiment of FIG. 47;

FIGS. 50C and 50D are views showing a pallet replacement operationsequence of the embodiment of FIG. 47;

FIG. 51 is a schematic perspective view showing an arrangement of amodification of the embodiment of FIG. 47;

FIG. 52 is a perspective view showing a case wherein an engaging hole isformed in the lower surface of a flange of a pallet;

FIG. 53 is a front view showing an arrangement of a lock mechanism forlocking a supporting position of a pallet in the pallet;

FIG. 54 is a side view of the lock mechanism shown in FIG. 53;

FIGS. 55A and 55B are flow charts showing a control program associatedwith a replenishment operation of a pallet to a buffer through anunmanned vehicle;

FIGS. 56A and 56B are views showing input displays in an operationassociated with manual replenishment of a pallet to the buffer; and

FIG. 56C is a view showing an operation sequence associated with manualreplenishment of a pallet to the buffer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An arrangement of an embodiment according to the present invention willbe described hereinafter with reference to the accompanying drawings.

The following description is made in the order of contents below.

TABLE OF CONTENTS

Schematic Arrangement

Description of Unmanned Vehicle

Description of Pallet

Arrangement of Pallet

Size of Pallet

Description of Buffer

Arrangement of Buffer Base

Arrangement of Separation Mechanism

Operation of Buffer

Basic Separating Operation

Position correction operation

Description of Elevator

Arrangement of Elevator Body

Arrangement of Replacing Mechanism

Operation of Replacing Mechanism

Take-in Operation from Buffer

Draw-in Operation of Empty Pallet

Push-out Operation of Pallet

Unloading Operation of-Empty Pallet

Description of Stocker

Arrangement of Stocker

Arrangement of Draw-out Unit

Arrangement of Lid Opening Mechanism

Operation of Lid Opening Mechanism

Operation of Draw-out Unit

Description of Robot

Arrangement of Robot

Operation of Robot

Operation of System

Arrangement of Control Unit

Inputting of Assembly Environment

Variation Factors of Parts Feeding Efficiency

Other Display Elements

Variables used in Control

Vertical Movement Range of Modules

Summary of Operation of Pallet Replacement

Detailed Description of each Module Control

Control of Robot and Stocker

Until Remaining Parts Count Becomes 1

When Remaining Parts Count Has Reached 1

Pallet Replacement

Pallet Separation by Buffer

Pallet Draw-out by Elevator

Elevator Replacement Standby Position

Movement to Standby Position

Detection of Remaining Parts Count 0

Stack of Empty Pallets

Replacement of Final Shelf

Queuing of Replacement Preparation Instruction

Initial Operating State Setting

Description of Modifications

Description of First Modification

Arrangement of Stack Separating Mechanism

Operation of Stack Separating Mechanism

Description of Second Modification

Description of Elevator

Description of Third Modification

Description of Replacing Mechanism

Control

Description of Fourth Modification

Arrangement

Control

Another Embodiment

Arrangement

Control

Modification of Another Embodiment

Others

Locking of Pallets in Stocker

Parts Replenishment to FAC

Replenishment by Unmanned Vehicle

Manual Replenishment

Effects of Embodiments

SCHEMATIC ARRANGEMENT

The schematic arrangement of a flexible assembling center (to bereferred to as an FAC hereinafter) 10 of this embodiment will bedescribed hereinafter with reference to FIGS. 1 and 2.

The FAC 10 comprises an automatic assembling device (to be referred tosimply as a robot hereinafter) 12 for automatically assembling apredetermined product from a plurality of parts x₁, x₂, x₃, . . . , aparts feeding system 14 for automatically feeding, to the robot 12 thenecessary parts x₁, x₂, x₃, . . . according to the assembling order, acontrol unit 16, connected to both the robot 12 and the parts feedingsystem 14, for driving and controlling them so that an assemblingoperation of the robot 12 can be efficiently executed, and aninput/output (I/O) device 18, connected to the control unit 16, withwhich assembling information data is input by an operator.

The parts feeding system 14 receives a variety of parts x₁, x₂, x₃, . .. stocked in an automated warehouse (not shown) through a plurality ofunmanned vehicles 20 (FIG. 1). More specifically, the parts feedingsystem 14 basically includes a buffer 22, a stocker 24, and an elevator26. Buffer 22 serves as a temporary storing means for receiving andtemporarily retaining the parts x₁ , x₂ , x₃ , . . . from the unmannedvehicles 20. Stocker 24, as means arranged adjacent to the robot 12,sequentially feeds parts necessary for assembly to the robot 12according to the assembling order. Elevator 26, disposed between thebuffer 22 and the stocker 24, as a specific form of transfer means,transfers the parts x₁, x₂, x₃, . . . , which are short in the stocker24, from the buffer 22 to the stocker 24.

DESCRIPTION OF UNMANNED VEHICLE

Unmanned vehicles 20 are equipped so as to selectively load, to thebuffer 22, parts x₁, x₂, x₃, . . . to be subjected to assembly among alarge number of parts x₁, x₂, x₃, . . . stocked in the unmannedwarehouse. More specifically, each unmanned vehicle 20 comprises arectangular parallel piped casing 28 constructed from frames, wheels 30attached to the lower surface of the casing 28, and pallet table 32mounted on the upper surface of casing 28, as schematically shown inFIG. 1. The wheels 30 are driven by a drive mechanism (not shown).

Each unmanned vehicle 20, upon driving of the wheels 30, travels betweenthe unmanned warehouse and buffer 22 along a road surfaced travel path.This travel state is optimally controlled by a production managementcomputer (to be described later). The selection operation of the partsx₁, x₂, x₃, . . . conveyed to buffer 22 and the placing operation ontoeach unmanned vehicle 20 are optimally controlled by the control unit 16mentioned above.

A plurality of pallets p₁, p₂, p₃, . . . respectively retaining partsx₁, x₂, x₃, . . . are stacked on the above-mentioned pallet table 32. Anempty pallet table 34 is provided on the lower surface of the casing 28so that a plurality of empty pallets p₁ ', p₂ ', p₃ ', . . . are stackedthereon. In the following description, unless otherwise specified,pallets in which at least one part is retained are represented by "p"without suffixes, and empty pallets are represented by "p'" withoutsuffixes.

The pallet table 32 has unloading rollers 32a for unloading the palletsp₁, p₂, p₃, stacked thereon and retaining the parts x₁, x₂, x₃, . . .The empty pallet table 34 has loading rollers 34a for loading emptypallets p₁ ', p₂ ', p₃ ', . . . stacked thereon. These unloading andloading rollers 32a and 34a are rotated by a drive motor (not shown).

DESCRIPTION OF PALLET Arrangement of Pallet

The parts x₁, x₂, x₃, . . . are retained in the corresponding palletsp₁, p₂, p₃, . . . The parts retained in the pallets p₁, p₂, p₃, . . .are stacked on each unmanned vehicle 20, and are temporarily stored inbuffer 22, which are then stocked in the stocker 24 through the elevator26. The parts x₁, x₂, x₃, . . . are then provided to the robot 12. Morespecifically, the pallets p₁, p₂, p₃, . . . retain identical types ofparts x₁, x₂, x₃, . . . As shown in FIG. 3, each pallet p includes apallet body 36 and flanges 38. Pallet body 36 with an open uppersurface, retains and then loads/unloads in avertical directioncorresponding parts x₁, x₂, x₃, . . . Flanges 38 are integrally moldedto extend outwardly at two side edges of the pallet body 36 along atleast the conveying direction d of the pallets p₁, p₂, p₃, . . . As canbe seen from an illustrated shape, the flanges 38 are actually formedaround the overall periphery of the pallet body 36. A lid 40 forremovably closing the upper open surface of the pallet body 36 is placedon the pallet body 36.

As shown in FIG. 3, first and second notches 38a and 38b are formed atboth end portions of each flange 38. A third notch 38c is formed at thecenter thereof. The first and second notches 38a and 38b are formed totake out pallets p₁, p₂, p₃, . . . from the buffer 22 to the elevator 26or to take them out or draw them in from the stocker 24 to the robot 12or the elevator 26. The central third notches 38c are formed so that alifting member (to be described later) is inserted therethrough to liftand then remove the lid 40 from pallet body 36. As a result, the palletbody 36 stocked in the stocker 24 can be taken out to the side of therobot 12 while the upper surface of the pallet body 36 is open.

Each of the first and second notches 38a and 38b is formed of a recesshaving a substantially isosceles trapezoidal shape in the plane, withthe shorter base defining the bottom of the recess.

More specifically, the lid 40 covers the opening of the upper surface ofthe corresponding pallet p₁, p₂, p₃, . . . until the final stage wherethe robot 12 handles the parts x₁, x₂, x₃, . . . , i.e., in other words,until the pallets p₁, p₂, p₃, . . . are moved to a draw-out standbyposition (to be described later) in the stocker 24. Thus, the parts x₁,x₂, x₃, . . . can be prevented from being contaminated with dust or thelike.

Size of Pallet

These pallets p₁, p₂, p₃, . . . are of three-types having thicknesses,i.e., 25 mm, 50 mm, and 100 mm in accordance with the parts to beretained, as shown in FIG. 4. In the following description, for the sakeof simplicity, small parts x₁, with a maximum number of 54, are retainedin the pallet p₁ having a thickness of 25 mm, medium parts x₂, with amaximum number of 38, are retained in the pallet p₂ having a thicknessof 50 mm, and large parts x₃, with a maximum number of 13, are retainedin the pallet p₃ having a thickness of 100 mm.

The thicknesses of the flanges 38 of the pallets p₁, p₂, p₃, arecommonly set to be 12 mm. A recess 36a is formed in the entire innerperiphery of each pallet body 36 to receive the lower portion of apallet body 36 immediately thereabove (indicated by a broken line inFIG. 5), thereby preventing lateral position shifting. The depth of therecess 36a is set to be 7 mm. In this manner, when the three types ofpallets p₁, p₂, and p₃ are stacked one by one, the height of this stackis set to be:

    25+50+100-7×2=1.61 mm

Note that a bar code B, indicating data of the type or number of partsx₁ , x₂ , x₃ , . . . retained in the corresponding one of the palletsp₁, p₂, p₃, . . . as well as the height data of the correspondingpallet, is printed on the side surface of the flange 38 of each of thepallets p₁, p₂, p₃, . . . , as shown in FIG. 3.

DESCRIPTION OF BUFFER

The buffer 22, for receiving and temporarily storing the pallets p₁, p₂,p₃, retaining the parts x₁, x₂, x₃, . . . from the pallet table 32 ofthe unmanned vehicle 20 arranged as described above, and for loadingempty pallets p₁, p₂, p₃, . . . to the unmanned vehicle 20, will bedescribed hereinafter with reference to FIG. 6.

Arrangement of Buffer Base

The buffer 22 has a base 42 fixed on a frame (not shown), columns 44a,44b, 44c, and 44d standing at the four corners of the base 42, andstanding plates 46a and 46b respectively standing and bridging the innersurfaces of the pair of columns 44a and 44b and the pair of columns 44cand 44d along the conveying direction d of the pallets p₁, p₂, p₃, . . .Guide members 48 are fixed along the vertical side edges of the opposingsurfaces of the standing plates 46a and 46b. A slidable member 50 isarranged along each guide member 48 to be vertically slidable. A bufferbase 52 is mounted to be supported by these four slidable members 50 atfour corners.

The buffer base 52 receives the pallets p₁, p₂, p₃, . . . retaining theparts x₁, x₂, x₃, . . . from the above-mentioned unmanned vehicle 20.Loading rollers 54 for receiving the pallets p₁, p₂, p₃, . . . stackedthereon and retaining the parts x₁, x₂, x₃, . . . are disposed on thebuffer base 52 so as to be rotatably supported by roller guides 56 atboth their ends. These loading rollers 54 are rotated by a drive motor(not shown).

A slit 58 extending in the vertical direction is formed in a portionsandwiched between the guide members 48 of the left standing plate 46bin FIG. 6. A projection 52a is integrally formed on the buffer base 52to extend through the slit 58.

The buffer base 52 is vertically movable to separate a pallet p in whichthe count of remaining parts x becomes 1 from the pallets p₁, p₂, p₃, .. . in the stocker 24, and to thereon replace p' with another pallet pso as to replenish the parts x.

More specifically, a servo motor M_(B) for moving the buffer base 52 inthe vertical direction along the guide members 48 is disposed betweenthe upper ends of the pair of columns 44c and 44d to which the far-sidestanding plate 46b is attached. The servo motor M_(B) comprises arotating shaft extending along the vertical direction, and the rotatingshaft is connected to rotate a ball screw 60 which is rotatably disposedbetween the columns 44c and 44d and extends along the verticaldirection. A portion midway along the ball screw 60 is held in thethreaded engagement with the above-mentioned projection 52a. In thismanner, when the rotating shaft of the servo motor M_(B) is rotated, theball screw 60 is rotated, thereby moving the buffer base 52 in avertical direction.

Note that an encoder 62 for detecting an angular position of the servomotor M_(B), i.e., the vertical position of the buffer base 52 isattached to the servo motor M_(B).

Arrangement of Separation Mechanism

With the above arrangement, the buffer base 52 can be vertically movedto an arbitrary vertical position. As described above, in order toseparate a specific pallet p from the pallets p₁, p₂, p₃, . . . stackedon the buffer base 52, the buffer 22 comprises a separation mechanism64.

The separation mechanism 64 comprises a pair of first separation pawls66 arranged at the upper end of each of the standing plates 46a and 46b,and a pair of second separation pawls 68 disposed below the firstseparation pawls 66 at a predetermined interval. Note that the first andsecond separation pawls 66 and 68 are arranged at the identical verticalpositions on both the standing plates 46a and 46b.

The first and second separation pawls 66 and 68 are arranged to becapable of hooking the flanges 38 of the pallets p₁, p₂, p₃, . . .stacked on the buffer table 52 from both sides. In other words, thefirst and second separation pawls 66 and 68 attached to the standingplates 46a and 46b are reciprocal between a projecting position at whichthe flanges 38 are hooked from below, and a retracted position at whichthe pawls are separated from the flanges 38.

More specifically, each pair of first separation pawls 66 integrallyhave supporting rods 70 extending through the corresponding standingplate 46a of 46b to the rear surface. The supporting rods 70 areintegrally connected through a connecting plate 72 at the rear surfaceof the standing plate 46a or 46b, as shown in FIG. 6. The connectingplate 72 is connected to a first air cylinder C_(B1) for reciprocatingthe first separation pawls 66. In this manner, the first separationpawls 66 are reciprocally driven between the projecting and retractedpositions upon driving of the first air cylinder C_(B1).

Since the structure for driving the second separation pawls 68 issubstantially the same as that for driving the first separation pawl 66(excepting that a second air cylinder C_(B2) is arranged as a drivesource), a detailed description thereof will be omitted.

The distance between the first and second separation pawls 66 and 68described above is set to be 110 mm, which is slightly larger than 100mm as the maximum height of the pallets p₁, p₂, p₃, . . .

A bar code reader 74 for reading the bar code B printed on the pallet pis arranged beside the pallet p which is hooked by the first separationpawls 66. Since the arrangement of the bar code reader 74 is known tothose who are skilled in the art, a description thereof will be omitted.

An unloading mechanism 76 is arranged on the base 42 to extend to thelower position of the elevator 26 (i.e., a position adjacent to thestocker 24). The unloading mechanism 76 is arranged to unload emptypallets p₁ ', p₂ ', p₃ ', . . . at the stocker 24 to the empty pallettable 34 of the unmanned vehicle 20 described above, and comprises aplurality of unloading rollers 78. These unloading rollers 78 arerotated by a drive motor (not shown).

The vertical position of the unloading mechanism 76 is set to be thesame as that of the empty pallet table 34 of the unmanned vehicle 20.The standby position of the buffer base 52 is set to be the same as thevertical position of the pallet table 32 of the unmanned vehicle 20.

OPERATION OF BUFFER Basic Separating Operation

An operation for separating a given pallet pa from the pallets p₁, p₂,p₃, . . . stacked on the buffer base 52 in accordance with a requestfrom the robot 12 (to be described later) will be described withreference to FIGS. 7A to 7D.

Assume that 12 pallets are stacked on the buffer base 52 in the order ofp₁, p₂, p₃, p₁, p₂, p₃, p₁, p₂, p₃, p₁, p₂, and p₃ from the lowerdirection, as shown in FIG. 7A. Note that pallets p₁, p₂, p₃, . . .having a total height of 800 mm can be stacked on the buffer base 52. Inthe above case, the 12 pallets have the total height of:

    (25+50+100)×4-7×11=623 mm

In this state, when a request for separating the pallet p₁ retaining theparts x₁ is sent from the robot 12, an instruction is supplied toseparate the third pallet p₁ from the top from the plurality of palletsp₁ stacked on the buffer base 52 according to the FIFO rule. In thefollowing description, the third pallet p₁ from the top is denoted byreference symbol pa, and a pallet immediately thereabove, i.e., thesecond pallet from the top is denoted by reference symbol pb.

As described above, when the request for separating the pallet pa issent from the robot 12, the buffer base 52 is moved (in this case, moveddownward) until the pallet pb stacked immediately above the pallet pa tobe separated is brought to a position where the pallet pb is hooked bythe first separation pawls 66, as shown in FIG. 7B. Note that the firstand second separation pawls 66 and 68 are moved to retracted positionsin an initial state.

In the state illustrated in FIG. 7B, the first air cylinder C_(B1) isactuated to bias and push out the first separation pawls 66 from theretrated position to the hooking position. Thus, the flanges 38 of thepallet pb can be hooked by the first separation pawls 66 from the lowerdirection.

Thereafter, as shown in FIG. 7C, the servo motor M_(B) is rotated so asto move the buffer base 52 downward by 94 mm from the state illustratedin FIG. 7B. As a result, the pallet pa is brought to the position whereit can be hooked by the second separation pawls 68, and the pallet pb ishooked by the first separation pawls 66. More specifically, the pallet(or pallets) located above the pallet pb are hooked by the firstseparation pawls 66.

In the state illustrated in FIG. 7C, the second air cylinder C_(B2) isactuated to bias and push out the second separation pawls 68 from theretracted position to the hooking position. Thus, the flanges 38 of thepallet pa can be hooked by the second separation pawls 68 from the lowerdirection.

Thereafter, as shown in FIG. 7D, the servo motor M_(B) is rotated tomove the buffer base 52 downward by 15 mm from the state illustrated inFIG. 7C. As a result, only the pallet pa is hooked by the secondseparation pawls 68, and the pallets located therebelow are brought to aposition separate from the pallet pa. In this manner, only the palletpa, hooked by the second separation pawls 68 (to be simply referred toas a separation position hereinafter) and separated from other pallets,is set in a state wherein it can be removed.

After the pallet pa separated in this manner is taken out to theelevator 24 (to be described later), all the pallets are returned to bestacked on the buffer base 52 in the initial state such that any palletcan next be separated.

In this return operation, the second air cylinder C_(B2) is operated toretract the second separation pawls 68 from the hooking position in amanner opposite to that described above. Thereafter, the servo motorM_(B) is rotated to move the buffer base 52 upward by 134 mm (i.e., avalue obtained by adding the thickness of the taken-out pallet pa, i.e.,25 mm to the stroke of the downward movement of the buffer base 52,i.e., 94+15=109 mm). Upon this upward movement, the uppermost pallet ofthe pallets stacked on the buffer 52 is brought to a state wherein itcarries and lifts the pallet pb hooked by the first separation pawls 66thereon.

In this state, the first air cylinder C_(B1) is operated to retract thefirst separation pawls 66 from the hooking position to the retractedposition in a manner opposite to that described above. As a result, thepallet pb and the pallet (or pallets) above the pallet pb hooked by thefirst separation pawls 66 are stacked on the pallets already stacked onthe buffer base 52, and thus, all the pallets are stacked on the bufferbase 52. This position serves as a standby position, and a nextseparation instruction from the robot 12 is waited for at this position.

Position Correction Operation of Pallet in Separating Operation

The above-mentioned operation of the buffer 22 is a basic operation,excluding the case in which the manufacturing margin of error of thepallets overaccumulates. More specifically, each pallet is allowed tohave a manufacturing margin of error of ±0.3 mm. Therefore, thismanufacturing margin of error can accumulate when a large number ofpallets are stacked on the buffer base 52, and the moving operation tothe hooking position of the pallet pb by the first separation pawls 66in the above-mentioned basic operation causes an error. Thus, the palletpb often cannot be accurately moved to the hooking position by the firstseparation pawls 66.

More specifically, assuming the worst case, since all the palletsstacked are pallets p₁ having a minimum thickness of 25 mm and themaximum height of the stack is 800 mm as described above, the maximumaccumulated margin of error is:

    800÷(25-7)×0.3=13.3 mm

When the vertical position is changed by the maximum accumulated marginof error, even if the servo motor M_(B) is rotated to move thepredetermined pallet pb to the hooking position of the first separationpawls 66 according to the above-mentioned basic operation, the pallet pbcannot be actually located to the hooking position due to the presenceof the margin of error described above.

For this reason, in this embodiment, a sensor 80 is attached to thestanding plate 46b so as to be opposite to the side surface of thepallet body 36 which is brought to the correct hooking position(theoretical) by the first separation pawls 66. The sensor 80 comprisesa known reflection-type photocoupler, i.e., a pair of light-emitting andlight-receiving elements although a detailed description thereof will beomitted. When the side surface of the periphery of the flange 38 of apallet is located opposite the sensor 80, the sensor 80 is turned onupon reception of light emitted from the light-emitting element. Whenthe side surface of the pallet body 36 is located opposite the sensor80, the sensor 80 cannot receive the light emitted from thelight-emitting element, and is turned off.

More specifically, as shown in FIG. 8A, the sensor 80 is arranged suchthat the pallet pb stacked on the pallet pa is brought to the hookingposition by the first separation pawls 66 in a state wherein the sensor80 detects the upper end face of the flange 38 of the pallet pa.

The movement control of the contents of the pallet pb to the hookingposition by the first separation pawls 66 in consideration of themanufacturing margin of error of the pallets using the sensor 80 will bedescribed hereinafter with reference to FIGS. 8A to 8E.

In the case of the pallet p₁ having a thickness of 25 mm, as shown inFIG. 8A, since the thickness of the flange 38 is 12 mm and a fittingmargin of 7 mm to the fitting recess 36a of the pallet body 36 locatedbelow is taken into consideration, a range of appearance of the sidesurface of the pallet body 36 is given by:

    25-12-7=6 mm

Therefore, regarding the maximum accumulated manufacturing margin oferror described above, three theoretical relative positionalrelationships between the pallets pa and pb which are moved by the servomotor M_(B) and the sensor 80 can be assumed as shown in FIGS. 8B, 8C,and 8D.

More specifically, three operational modes occur, including a first modewherein the periphery of the flange 38 of the pallet pa to be separated(in other words, the pallet pa hooked by the second separation pawls 68)opposes the sensor 80, as shown in FIG. 8B, a second mode wherein theperiphery of the flange 38 of the pallet pb to be hooked by the firstseparation pawls 66 opposes the sensor 80, as shown in FIG. 8C, and athird mode wherein the side surface of the pallet body 36 of the palletpb to be hooked by the first separation pawls 66 opposes the sensor 80,as shown in FIG. 8D.

When the periphery of the flange 38 of the pallet is located adjacent tothe sensor 80, the sensor 80 is turned on. In this ON state, the firstand second modes shown in FIGS. 8B and 8C are considered. For thisreason, the buffer base 52 is moved downward until the sensor 80 detectsthe upper end face of the flange 38, i.e., the sensor 80 is turned off,as shown in FIG. 8E.

When the sensor 80 is turned off, the bar code B which is printed to thepallet the upper surface of which is detected is read through the barcode reader 74. As a result, where the pallet is determined that it isthe pallet pa which should be separated, upon reading the bar code B,the pallet pb which is disposed on the pallet pa which should beseparated is brought to the hooking position of the first separationpawls 66, as mentioned before. In accordance with the aforementionedbasic operation, the first air cylinder C_(B1) is then actuated, so thatthe first separation pawls 66 are pushed out to the hooking position.

Upon reading the bar code B printed on the pallet whose upper end faceis detected if it is determined that this pallet is not the pallet pa tobe separated, it is automatically determined that this pallet whose barcode B is read is the pallet pb immediately above the pallet pa.Therefore, the servo motor M_(B) is rotated so that the buffer base 52is moved upward by the height of the pallet pb. In this manner, thesensor 80 detects again the upper end face of the flange 38, as shown inFIG. 8E. The pallet having the flange 38 whose upper end face isdetected should be the pallet pa to be separated. After this fact isconfirmed through the bar code reader 74, the first air cylinder C_(B1)is actuated in accordance with the above-mentioned basic operation, sothat the first separation pawls 66 are pushed out to the hookingposition.

If upon reading the bar code B of the detected pallet which was movedupward it is determined that the pallet is not the pallet pa to beseparated, a control error may occur or a pallet different from arequested pallet may be conveyed by the unmanned vehicle 50 from theunmanned warehouse. Thus, at this time, the control operation isstopped, and a predetermined warning operation is started.

When the side surface of the pallet body 36 is located opposite thesensor 80, i.e., the pallet is moved according to the calculated value,the sensor 80 is turned off. In this OFF state, only the third modeshown in FIG. 8C is considered. For this reason, the buffer base 52 ismoved upward until the sensor 80 detects the upper end face of theflange 38, i.e., the sensor 80 is turned on, as shown in FIG. 8E.

When the sensor 80 is turned on, the bar code B printed on the palletwhose upper end face is detected is read through the bar code reader 74.When a pallet to be separated is confirmed as the pallet pa according tothe read bar code B, the pallet pb stacked on the pallet pa to beseparated has reached the hooking position of the first separation pawls66. Therefore, the first air cylinder C_(B1) is started and the firstseparation pawls 66 are pushed out to the hooking position in accordancewith the basic operation described above.

When the above described position correction operation of the pallet isexecuted, even if accumulation of the manufacturing margin of error ofthe pallets occurs, a state wherein the pallet pb, stacked on the palletpa to be separated, can be reliably hooked by the first separation pawls66 can be achieved.

DESCRIPTION OF ELEVATOR

The arrangement of the elevator 26, disposed between the buffer 22 andthe stocker 24 and used for replacing the empty pallets p'in the stocker24 with the pallets p filled with parts x, will be described hereinafterwith reference to FIGS. 9 to 13G.

Arrangement of Elevator Body

As shown in FIG. 9, this elevator 26 is disposed on a base 142 common tothe stocker 24 (to be described later). A pair of columns 82a and 82bare adjacent to the columns 44a and 44b of the buffer 22 on the side ofthe robot 12 (see FIG. 2) and a pair of columns 82c and 82d areseparated by a predetermined distance from the robot 12 and provided ona portion of the base 142. The upper ends of these four columns 82a,82b, 82c, and 82d are coupled to each other by coupling members 84. Notethat the coupling members 84 are also arranged common to the stocker 24(to be described later).

An elevator body 86 is provided to be vertically movable and positionedbetween the pair of columns 82a and 82c and the pair of columns 82b and82d along the conveying direction d.

The elevator body 86 comprises a box-like member in which a pair ofsurfaces perpendicular to the conveying direction of the pallets p₁, p₂,p₃, . . . are open. The elevator body 86 receives the pallet paseparated at the separation position from the buffer 22 based on arequest from the robot 12 (a request issued when the count of the partsremaining in a predetermined pallet becomes "1"), and holds the palletpa therein. The elevator 86 transfers the held pallet pa to the stocker24 in accordance with a request from the stocker 24 (a request issuedwhen the last part described above is used for assembly, and hence, noparts are present). Guide members 88 are vertically fixed to theopposing surfaces of the pair of columns 82a and 82c and those of thepair of columns 82b and 82d along the conveying direction d of thepallets p₁, p₂, p₃, . . . A pair of slidable members 90 are attached toeach of the guide members 88 to be movable in the vertical direction andto be separated in the vertical direction by a predetermined distance.The above-mentioned elevator body 86 is mounted to be supported at fourcorners by the four slidable members 90 present in the above horizontalplane and by the four slidable members 90 present in a horizontal planetherebelow.

A gap extending in the vertical direction is defined in a portionsandwiched between the far-side pair of columns 82b and 82d in FIG. 9. Aprojection (not shown) is integrally formed with the elevator body 86 soas to extend into the gap.

A servo motor M_(E1) for moving the elevator body 86 in the verticaldirection along the guide members 88 is disposed on a portion of thecoupling member 84 for coupling the upper end of the far-side pair ofcolumns 82b and 82d. The servo motor M_(E1) comprises a rotating shaftextending in the vertical direction. The rotating shaft is connected torotate a ball screw 92 which is rotatably disposed between the columns82b and 82d and extends in the vertical direction. A portion midwayalong the ball screw 92 is threadably engaged with the projectiondescribed above. In this manner, upon rotation of the rotating shaft ofthe servo motor M_(E1), the ball screw 92 is rotated, and hence, theelevator body 86 is moved in the vertical direction.

An encoder 94 for detecting the angular position of the servo motorM_(E1), i.e., the vertical position of the elevator body 86, is attachedto the servo motor M_(E1). With this arrangement, the elevator body 86can be vertically moved to an arbitrary vertical position.

Arrangement of Replacing Mechanism

The elevator body 86 which is vertically movable as described abovecomprises a replacing mechanism 96 for taking therein a pallet pa filledwith parts and separated from the buffer 22, pushing out this pallet patherefrom, and drawing an empty pallet p' therein from the stocker 24.

The replacing mechanism 96 includes a servo motor M_(E2) as a drivesource which is fixed on the upper surface of the elevator body 86through a stay 98. The drive shaft of the servo motor M_(E2) is fixed toone end of a swingable arm 100. Thus, upon rotation of the drive shaft,the swingable arm 100 is swung in the horizontal plane. An elongatedgroove 100a is formed at the mid point of the swingable arm 100 alongits longitudinal direction. A guide groove 102 extending in theconveying direction d is formed in the upper surface portion of theelevator body 86 over a range corresponding to the swinging range of theswingable arm 100. The guide groove 102 is formed over the entire lengthof the elevator body 86 along the conveying direction d.

A guide pin 104 is arranged to be commonly inserted through theelongated groove 100a and the guide groove 102 in the verticaldirection. The head portion of the guide pin 104 has a larger diameterthan the other portions, and can be prevented from being disengaged fromthese grooves 100a and 102. With this structure, when the servo motorM_(E2) is reciprocally pivoted, the swingable arm 100 is swung, andhence, the guide pin 104 is reciprocated along the guide groove 102,i.e., the conveying direction d.

As shown in FIGS. 10 to 12, a slide plate 106 is fixed to the lower endof the guide pin 104 so as to be located in the elevator body 86. Theslide plate 106 is attached to the guide pin 104 so as to extend along adirection perpendicular to the conveying direction d. First hooks 108are mounted on both end portions of the side surface of the slide plate106 through first hook slide members 110 so as to be slidable along thelongitudinal direction of the slide plate 106, i.e., a directionperpendicular to the conveying direction d. The pair of first hooks 108are formed into shapes capable of being engaged, from both sides, withthe first notches 38a formed in the flanges 38 on the side of theelevator 26 of each of the pallets p₁, p₂, p₃, . . . More specifically,the distal end portion of each first hook 108 has an isoscelestrapezoidal shape complementarily coinciding with that of the notch.

Air cylinder supporting plates 112 are respectively fixed to both endsof the slide plate 106 so as to extend along the conveying direction d.A first air cylinder C_(E1) for reciprocating the corresponding firsthook 108 is mounted at the end portion of each air cylinder supportingplate 112 on the side of the buffer 22. The distal end portion of afirst piston 114 of each first air cylinder C_(E1) is connected to thecorresponding first hook 108. In this manner, upon driving of the firstair cylinders C_(E1), the first hooks 108 are reciprocated to be engagedwith or disengaged from the first notches 38a of the flanges 38.

Second hooks 116 are mounted on both end portions of the side surface onthe side of the stocker 24 of the slide plate 106 through second hookslide members 118 so as to be slidable along the longitudinal directionof the slide plate 106, i.e., a direction perpendicular to the conveyingdirection d. The pair of second hooks 116 are formed into shapes capableof being engaged from both sides with the second notches 38b formed inthe flanges 38 on the side of the unmanned vehicle 20 of each of thepallets p₁, p₂, p₃, . . .

Second air cylinders C_(E2) for reciprocating the second hooks 116 aremounted on the end portions on the side of the stocker 24 of the aircylinder supporting plates 112 fixed to both ends of the slide plate106. The distal end portion of a second piston 120 of each second aircylinder C_(E2) is connected to the corresponding second hook 116described above. In this manner, upon the driving of the second aircylinders C_(E2), the second hooks 116 are reciprocated so as to beengaged with or disengaged from the second notches 38b of the flanges38.

A pair of stationary slide guides 122 for slidably supporting the palletp, engaged with first or second hooks 108 or 116 and drawn in/pushed outin accordance with the pivotal motion of the servo motor M_(E2), aredisposed on the lower surface of the elevator body 86. Morespecifically, the upper surfaces of the stationary slide guides 122 areslidable relative to the lower surplices of the flanges 38 at both sidesof the drawn-in/pushed-out pallet p.

The height of the upper edge of each stationary slide guide 122 is setto slidably support the pallet p₃ having a height of 100 mm as a maximumheight. The standby position of the elevator body 86 is set at thevertical position where the upper end faces of the stationary slideguides 122 can horizontally receive the pallet pa at the separationposition.

Third hook mounting plates 124 are fixed to the lower portions of theair cylinder supporting plates 112 so as to extend along the extendingdirection of the slide plate 106. Third hooks 126 are mounted on bothend portions of the side surfaces on the side of the stocker 24 of themounting plates 124 through third hook slide members (not shown) alongthe longitudinal direction of the slide plate 106, i.e., a directionperpendicular to the conveying direction d. The pair of third hooks 126are formed into shapes capable of being engaged, from both sides, withthe second notches 38b of the flanges 38 of each of the empty pallets p₁', p₂ ', p₃ ', . . . in the stocker 24.

Third air cylinders C_(E3) for reciprocating the third hooks 126 areattached to the lower end portions of the air cylinder supporting plates112 fixed to both ends of the slide plate 106. The distal end portion ofa third piston 130 of each third air cylinder C_(E3) is connected to thecorresponding third hook 126. In this manner, upon the driving of thethird air cylinders C_(E3), the third hooks 126 are reciprocated so asto be engaged with or disengaged from the second notches 38b of theflanges 38.

Note that the third hooks 126 extend below the elevator body 86 throughguide grooves 132 (FIG. 9) formed in the lower surface of the elevatorbody 86 along the conveying direction d. A pair of movable slide guides134 for slidably receiving the pallet p' taken out from the stocker 24by the third hooks 126 are disposed on the lower surface of the elevatorbody 86.

The movable slide guides 134 are arranged to be movable along adirection perpendicular to the conveying direction d, i.e., to beseparated from the empty pallet p' received therein, so as to stack theempty pallet p' received therein onto the unloading rollers 78 (see FIG.6) of the unloading mechanism 76 described above. More specifically, asshown in FIGS. 10 and 11, the movable slide guides 134 are reciprocallymounted on the lower surface of the elevator body 86 through slidemembers 136. Air cylinder supporting plates 138 are fixed to both sidesof the lower surface of the elevator body 86. Fourth air cylindersC_(E4) for reciprocating the movable slide guides 134 are mounted on theair cylinder supporting plates 138, respectively. The distal end portionof a fourth piston 140 (not shown) of each fourth air cylinder C_(E4) isconnected to the corresponding movable slide guide 134 described above.In this manner, upon the driving of the fourth air cylinders C_(E4), themovable slide guides 134 are reciprocated so as to be engaged with ordisengaged from the flanges 38 of the empty pallet p'.

Operation of Replacing Mechanism

A replacing operation of the pallets p and p' in the replacing mechanism96 with the above arrangement will be described hereinafter withreference to FIGS. 13A to 13G.

In the initial state, the vertical position of the elevator body 86 isset so that the upper end face of each stationary slide guide 122 hasthe same height as that of each second separation pawl 68 of the buffer22. The initial condition of the replacing mechanism 96 is set such thatthe swingable arm 100 is located at the middle position of the guidegroove 102, as shown in FIG. 9. No compressed air is supplied to the aircylinders C_(E1), C_(E2), C_(E3), and C_(E4). The corresponding hooks108, 116, and 126, and the movable slide guides 134 are kept retractedat the corresponding retracted positions.

Take-in Operation from Buffer

When the initial state is set, an operation for separating apredetermined pallet pa in the buffer 22 is started based on a requestfrom the robot 12, i.e., a request for replacing preparation when thecount of remaining parts x in a predetermined pallet p in the stocker 24has reached 1. Also, in the elevator 26, an operation for taking thepallet pa separated in the buffer 22 into the elevator body 86 isexecuted.

More specifically, when the above-mentioned request is issued from therobot 12, the servo motor M_(E2) is rotated in a direction indicated byan arrow A in FIG. 9 from the state illustrated in FIG. 13A so as tocause the replacing mechanism 96 to move toward the buffer 22 in theelevator 26. Upon this movement, as shown in FIG. 13B, the first hooks108 of the replacing mechanism 96 on the side of the buffer 22 areallowed to be engaged from both sides with the first notches 38a on theside of the elevator 26 formed in the flanges 38 of the pallet pa to beseparated at the separation position in the buffer 22. Note that in theengaging state of the first hooks 108, the first hooks 108 are set notto interrupt the separation operation in the buffer 22.

In this state, the operation of the elevator 26 is set in a take-instandby state, and the take-in standby state is maintained until theseparating operation in the buffer 22 is completed. Upon completion ofthe separation operation, i.e., when a separation completion signal isissued from the buffer 22, the replacing mechanism 96 starts the take-inoperation of the separated pallet pa in response to the outputting ofthe separation completion signal.

More specifically, compressed air is supplied to the first air cylindersC_(E1), so that the first hooks 108 are engaged, from both sides, withthe first notches 38a formed in the flanges 38 of the separated palletpa. Thereafter, the servo motor M_(E2) rotates the swing arm 100 in adirection indicated by an arrow B in FIG. 9, so as to take guide pin 104of the replacing mechanism 96 in the elevator body 86 along theconveying direction d. As shown in FIG. 13C, in a state wherein thepallet pa has completely been taken in the elevator body 86, theoperation of the servo motor M_(E2) is stopped, and thereafter, thesupply of the compressed air to the first air cylinders C_(E1) arestopped, and then the first air cylinders C_(E1) are operated so thatthe first hooks 108 are disengaged from the first notches 38a of thepallet pa.

In this manner, the pallet pa separated in the buffer 22 is wholly takeninto the elevator 26. In this take-in state, the replacing mechanism 96is brought to a state wherein it partially extends from the elevatorbody 86 toward the stocker 24 as shown in FIG. 13C. The servo motorM_(E2) is rotated in a direction indicated by the arrow A, so that thereplacing mechanism 96 is returned to be completely stored in theelevator body 96, as shown in FIG. 13D.

Draw-in Operation of Empty Pallet

Thereafter, the servo motor M_(E1) rotates, so that the elevator body 86is moved downward to a position for drawing in an empty pallet p'retaining no parts x among pallets p stocked in the stocker 24. Theelevator body 86 stands by at this draw-in position waiting for areplacing request of the empty pallet p' from the stocker 24.

Note that the draw-in position is defined as a position above a feedposition of the pallet p to the robot 12 in the stocker 24 (to bedescribed later) by a distance corresponding to one pallet which hascompleted feeding of parts to the robot 12. As described above, sincepallets p having three different heights are prepared, three draw-inpositions are defined in accordance with a difference in heights.

The standby position of the elevator body 86 is set to be a verticalposition such that the third hooks 126 of the replacing mechanism 96 canbe engaged with the second notches 38b of the flanges 38 of the palletp' located at the draw-in position. In this manner, the draw-in standbyposition of the empty pallet p' in the elevator 26 is defined.

In the replacing mechanism 96 in the elevator body 86 brought to thedraw-in standby position, as described above, the pallet pa retaining acomplete set of parts x is held on the pair of stationary slide guides122.

At this draw-in standby position, when the empty pallet p' is moved tothe draw-in position in the stocker 24, the servo motor M_(E2) rotatesthe swing arm 100 in the direction indicated by the arrow B. The thirdhooks 126 of the replacing mechanism 96 are thereby moved to positionscapable of being engaged with the second notches 38b formed in theflanges 38 of the empty pallet p' at the draw-in position, as shown inFIG. 13E. Thereafter, compressed air is supplied to the third and fourthair cylinders C_(E3) and C_(E4), so that the third hooks 126 are engagedwith the second notches 38b of the empty pallet p'. At the same time,the movable slide guides 134 are pushed out below the elevator body 86so as to be capable of supporting the drawn-in empty pallet p'.

Thereafter, the servo motor M_(E2) rotates the swing arm 100 in thedirection indicated by the arrow A to draw the empty pallet p' in aportion below the elevator body 86. In this manner, the empty pallet p'is held below the elevator body 86 while being supported on the movableslide guides 134, as shown in FIG. 13F, thus completing the draw-inoperation of the empty pallet p'. Then, the third air cylinders C_(E3)are actuated to cause the third hooks 126 to be disengaged from thesecond notches 38b of the empty pallet p'.

Push-out Operation of Pallet

In the draw-in state of the empty pallet p', the second hooks 116 of thereplacing mechanism 96 are allowed to be engaged with the second notches38b of the pallet pa supported on the stationary slide guides 122.Therefore, compressed air is supplied to the second air cylinders C_(E2)to cause the second hooks 116 to be engaged with the second notches 38bof the pallet pa.

Simultaneous with the engaging operation of the second books describedabove, the servo motor M_(E1) in the elevator 26 rotates to move theelevator body 86 downward, so that the pallet pa therein is brought to aposition horizontally opposing the draw-in position in the stocker 24.The servo motor M_(E2) rotates the swing arm 100 in the directionindicated by the arrow B to push out the pallet pa from the elevatorbody 86 to an available retaining position of the stocker 24, as shownin FIG. 13G. Thereafter, the second air cylinders C_(E2) are operated toseparate the second hooks 116 from the second notches 38b of the palletp. Then the servo motor M_(E2) rotates in the direction indicated by thearrow A, to draw the replacing mechanism 96 in the elevator body 86. Inthis manner, the push-out operation of the pallet p to the stocker 24 iscompleted.

Unloading Operation of Empty Pallet

After the empty pallet p' is replaced with the pallet pa filled withparts x, as described above, the drawn empty pallet p' is supportedbelow the elevator body 86. Therefore, in order to stack the emptypallet p' on the unloading rollers 78 of the unloading mechanism 76, thepulse motor M_(E1) is rotated to move the elevator body 86 downward.Thus, when no empty pallet p' is stacked on the unloading rollers 78,the empty pallet p' is moved to a position immediately above theunloading rollers 78. When the empty pallet p' (or pallets p') hasalready been stacked on the unloading rollers 78, the empty pallet p' tobe stacked is moved to a position immediately above the already stackedpallet p' (or the uppermost pallet of stacked pallets p'). Thereafter,the fourth air cylinders C_(E4) are actuated to retract the movableslide guides 134, so that the empty pallet p' supported by the elevatorbody 86 falls down and is stacked on the unloading rollers 78 (or on theuppermost pallet of stacked pallets p'γ.

When the number of empty pallets p' stacked on the unloading rollers 78in this manner has reached a predetermined value, the unloading rollers78 are rotated, so that the stack of the empty pallets p' is conveyed toa position below the buffer base 52. The stack is then unloaded onto theempty pallet table 34 of the unmanned vehicle 20. In this manner, aseries of empty pallet unloading operations is completed.

In the elevator 26 after the empty pallet p' is discharged onto theunloading mechanism 76, the servo motor M_(E1) is rotated so as to movethe elevator body 86 upward to the above-mentioned initial position,i.e., a position horizontally opposing the separation position in thebuffer 22. The elevator then wait for the next operation.

DESCRIPTION OF STOCKER

The arrangement of the stocker 24, arranged adjacent to the robot 12,for sequentially feeding parts x₁, x₂, x₃, . . . necessary for assemblyto the robot 12 according to the assembly order will be describedhereinafter with reference to FIGS. 14 to 16

Arrangement of Stocker

The stocker 24 as shown in FIG. 14, comprises the base 142 fixed on afoundation (not shown), and common to the elevator 26 described above,columns 144a, 144b, 144c, and 144d standing at four corners of the base142, and coupling frames 84 for coupling upper ends of these columns144a, 144b, 144c, and 144d. Guide members 148 extending in the verticaldirection are fixed to opposing surfaces of the pair of columns 144a and144b on the side of the elevator 26 and the pair of columns 144c and144d on the side of the robot 12. A slidable member 150 is verticallyand movably attached to each guide member 148. An elevating frame 152 ismounted to be supported at four corners by these four slidable members150.

The elevating frame 152 stocks a stack of a plurality of pallets p,which are pushed out from the elevator 26 and drawn out to a draw-outunit 154 (to be described later). The stocker 24 is constructed so as tobe capable of drawing out the pallet one by one from the draw-outstandby position (to be described later). A plurality of shelves 156 forhooking the flanges 38 of the pallets p are disposed on the innersurfaces of the elevating frame 152 along the conveying direction d. Theshelves 156 extend horizontally, and are disposed at equal intervals ofabout 30 mm along the vertical direction.

As shown in FIG. 14, a notch 158 is formed at the central portion (inother words, a portion corresponding to the third notch 38c formed atthe center of the flange 38 of the pallet p stacked on each shelf 156)of each shelf 156. More specifically, the notch 158 is formed so as tobe capable of inserting therethrough a lifting arm 160 of an openingmechanism 170 (FIG. 15; to be described later) for opening the lid 40 ofthe pallet p to be drawn out to the draw-out unit 154.

A gap extending in the vertical direction is defined in a portionsandwiched between the far-side pair of columns 144c and 144d in FIG.14. A projection 162 is integrally formed with the elevating frame 152to extend into the gap.

A servo motor M_(S1) for moving the elevating frame 152 in the verticaldirection along the guide members 148 is disposed on a portion of thecoupling frame 84 which couples the upper ends of the far-side pair ofcolumns 144c and 144d. The servo motor M_(S1) comprises a rotating shaftextending in the vertical direction. The rotating shaft is connected torotate a ball screw 164 rotatably disposed between the columns 144c and144d and extending along the vertical direction. A portion midway alongthe ball screw 164 is threadably engaged with the projection 162. Inthis manner, upon rotation of the rotating shaft of the servo motorM_(S1), the ball screw 164 is rotated, thus moving the elevating frame152 in the vertical direction. Note that the feed amount of the verticalmovement of the elevating frame 152 is set to correspond to an integermultiple of 30 mm as a disposition pitch of the shelves 156.

An encoder 68 is attached to the servo motor M_(S1) so as to detect itsangular position, i.e., the vertical position of the elevating frame152. With the above arrangement, the elevating frame 152 can bevertically moved to an arbitrary vertical position.

Arrangement of the Draw-out Unit

The arrangement of the draw-out unit 154 described above will bedescribed below with reference to FIG. 14.

The draw-out unit 154 is provided to hold a pallet p retaining parts xused for assembly in the robot 12, which is received from the elevatingframe 152. The basic draw-out unit 154 includes a draw-out base 168fixed at a predetermined vertical position from the foundation (notshown), and a draw-out/draw-in mechanism 172, arranged on the draw-outbase 168 for draw-out/draw-in the pallet p from which the lid 40 isremoved by the lid opening mechanism 170 (to be described later; FIG.15).

The draw-out base 168 is horizontally fixed through a pair of supportingstays 174 respectively fixed to the surfaces of the columns 144a and144c on the side of the robot 12. A stopper 176 is attached to thedistal end portion of the draw-out base 168 on the side of the robot 12.The drawn pallet p abuts against the stopper 176 to define the draw-outposition of the pallet p. A pair of slide guides 178 extending along theconveying direction d are arranged at both sides of the draw-out base168. The upper end faces, i.e., the slide supporting surfaces of theseslide guides 178 are set to horizontally match the corresponding shelves156 of the elevating frame 152 in a stopped state during an intermittentfeed operation. Note that a pallet p which is supported by the shelves156 horizontally matching the slide guides 178 is defined as a palletlocated at the draw-out standby position.

The draw-out/draw-in mechanism 172 described above includes guidemembers 180 which are symmetrically disposed on both side portions ofthe draw-out base 168 and which extend on the side edges of the draw-outbase 168 along the conveying direction d, slidable members 182 slidablyattached to the corresponding guide members 180, and supporting plates184 fixed to the upper surfaces of the corresponding slidable members182. Hooks 186 which can be engaged with the first notches 38a formed inthe flanges 38 of the pallet p located at the draw-out standby positionin the elevating frame 152 are provided on the corresponding supportingplates 184 so as to be retractable in a direction perpendicular to theconveying direction d.

Air cylinders C_(S1) for retractably driving the hooks 186 are mountedon the supporting plates 184 so as to be located outside the hooks 186.A piston of each air cylinder C_(S1) is connected to the-correspondinghook 186. When compressed air is supplied to the air cylinders C_(S1),the hooks 186 are pushed to positions for engaging with the notches 38a.

Driving rollers 188 are rotatably supported on the distal end portionsof the side edges of the draw-out base 168 on the side of the robot 12,and idle rollers 90 are rotatably supported on the proximal end portionson the side of the elevator 26 thereof. An endless belt 92 is loopedaround the driving roller 188 and the idle roller 190 at each side edge.When the driving roller 188 is rotated, the endless belt 192 travels.The driving rollers 188 at both side edges are rotated together througha coupling shaft 194.

The supporting plate 184 at each side edge is fixed to the correspondingendless belt 192. Along with the travel of the endless belt 192, thesupporting plate 184 is reciprocally moved on the draw-out base 168along the conveying direction d. A driven roller 196 is coaxially fixedto the corresponding driving roller 188. A servo motor M_(S2) (notshown) is attached below the central portion of the side edge of thedraw-out base 168 through a stay 198. Driving rollers 202 are coaxiallyfixed to the driving shaft 200 of the servo motor M_(S2). An endlessbelt 204 is looped around the driving roller 202 and the driven roller196.

With the above arrangement, when the servo motor M_(S2) is driven, thedriving rollers 188 and 202 are rotated, and the endless belts 192travel accordingly. Thus, the hooks 186 are reciprocally moved along theconveying direction d.

Arrangement of Lid Opening Mechanism

The lid opening mechanism 170 will be described below with reference toFIGS. 15 and 16. Prior to the operation of draw-out/draw-in mechanism172 for drawing out the pallet p from the draw-out standby position inthe elevating frame 152 to the draw-out position on the draw-out base168, the lid opening mechanism 170 lifts up the lid 40 capped on onlythe pallet p. In other words, the pallet p, in which the parts x areretained, can be taken out by the robot 12 and drawn out to the draw-outposition on the draw-out base 168.

As shown in FIG. 15, the lid opening mechanism 170 includes aircylinders C_(S2) mounted on the side surfaces (on the side of theelevator 26) of the pair of columns 144a and 144c on the side of therobot 12, and lift-up arms 160 attached to the distal ends of pistons206 of the air cylinders C_(S2). Each air cylinder C_(S2) is obliquelymounted such that the sliding direction of its piston 206 is inclinedupward at about 45 degrees from the horizontal direction toward theelevating frame 152.

The lift-up arm 160, attached to the distal end of each piston 206, isconstituted by a body portion 160a and a projecting portion 160c. Bodyportion 160a is fixed to the piston 206 and extends along the extendingdirection of the piston 206. Projecting portion 160c is integrallyformed with the distal end of the body portion 160a, has a horizontalupper surface 160b, and projects upward outside the upper surface 160b.

Each air cylinder C_(S2) has two compressed air input terminals 208a and208b. When compressed air is supplied to one input terminal 208a, theair cylinder C_(S2) retracts the piston 206, so that the distal end ofthe lift-up arm 160 is deviated to a retracted position separated fromthe lid 40. When compressed air is supplied to the other input terminal208b, the cylinder C_(S2) pushes out the piston 206, so that the distalend of the lift-up arm 160 is deviated to a push-out position to beengaged with the lid 40.

The position, i.e., the vertical position, of the air cylinder C_(S2)with the above arrangement is set such that the upper surface 160b atthe distal end of the lift-up arm 160 at the push-out position can passthrough the third notch 38c formed in the flange 38 of the pallet p atthe draw-out standby position and can be engaged therewith from thelower side.

Operation of Lid Opening Mechanism

In the lid opening mechanism 170 with the above arrangement, when it isdetected that the pallet p has reached the draw-out standby position inaccordance with vertical movement of the elevating frame 152, theoperation of the lid opening mechanism 170 is started for the pallet p.More specifically, compressed air is supplied to the second inputterminals 208b of both the air cylinders C_(S2), and the pistons 206 arepushed out obliquely upward.

As a result, the distal ends of the lift-up arms 160 connected to thedistal ends of the pistons 206 pass through the third notches 38c formedat the center of the corresponding flanges 38 of the pallet p located atthe draw-out standby position, and the upper surfaces 160b at the distalends of the lift-up arms 160 respectively engage both side edges of thelid 40 from the lower side to lift up the lid 40 from the pallet p. Inthis manner, as shown in FIG. 16, the lid 40 is deviated to be separatedupward from the pallet p located at the draw-out standby position.Therefore, this pallet p can be drawn out to the draw-out position.

On the other hand, when the take-out operation of part (or parts) x bythe robot 12 is completed in the pallet p which is drawn out to thedraw-out position, this pallet p is then returned (drawn-in) to thedraw-out standby position. When the pallet p is returned to thisposition, compressed air is supplied to the first input terminals 208aof the air cylinders C_(S2). In this manner, the lift-up arms 160 arepushed obliquely downward, and during the push-down operation, the lid40 is capped on the pallet p to cover the upper surface of the pallet preturned to the draw-out standby position. In this manner, a series oflid opening operations are completed.

Operation of Draw-out Unit

A draw-out/draw-in operation for drawing out the pallet p, from whichthe lid 40 is removed by the lid opening mechanism 170, from thedraw-out standby position to the draw-out position and then drawing-in(returning) the pallet p to the original draw-out standby position inthe draw-out unit 154 will be described below.

In the initial state, the hooks 186 are moved in a direction opposite tothe conveying direction d upon driving of the servo motor M_(S2) so asto be brought to a position at which the hooks 186 can be engaged withthe first notches 38a of the flanges 38 of the pallet p.

From this initial state, as soon as the push-up operation of the lid 40is started, the air cylinders C_(S1) are operated, so that the hooks 186are engaged with the first notches 38a of the pallet p located at thedraw-out standby position. Thereafter, upon completion of the push-upoperation of the lid 40, the servo motor M_(S2) is rotated in adirection opposite to that described above, and as a result, the hooks186 are moved along the conveying direction d. More specifically, thepallet p with which the hooks 186 are engaged and which is located atthe draw-out standby position is drawn out from the elevating frame 152onto the draw-out base 168. The drawn pallet p slides along the pair ofslide guides 178.

The pallet p sliding along the slide guides 178 and drawn out along theconveying direction d abuts against the stopper 176 and is then stopped.Driving of the servo motor M_(S2) is also stopped. In this manner, thepallet p is held at the draw-out position.

Thereafter, the take-out operation of the part (or parts) x from thepallet p brought to the draw-out position is performed by the robot 12(to be described later). Upon completion of the take-out operation, theservo motor M_(S2) is again rotated in the reverse direction, so thatthe hooks 186 are moved in a direction opposite to the conveyingdirection d. In this manner, the pallet p is drawn-in (returned) andloaded onto the elevating frame 152. When the pallet p has completelybeen returned inside the elevating frame 152, driving of the servo motorM_(S2) is stopped. Thus, the pallet p is held in the elevating frame152.

Thereafter, the capping operation of the lid 40 in the above-mentionedlid opening mechanism 170 is executed, thus completing a series ofdraw-out/draw-in operations.

DESCRIPTION OF ROBOT

The arrangement of the robot 12 for receiving parts x fed from the partsfeeding system 14 (equipped with the above-mentioned buffer 22, elevator26, and stocker 24) and for assembling a predetermined product will beschematically described below with reference to FIGS. 1 and 2.

Arrangement of Robot

As shown in FIG. 2, the robot 12 includes a horizontal assembling stage210 having a portion located below the draw-out unit 154 of the stocker24. A pair of frames 212 stand at one side of the assembling stage 210.An X-axis robot arm 214 for defining the X-axis (an axis extending in adirection parallel to the conveying direction d) of the robot 12 isbridged on the frames 212. One end of a Y-axis robot arm 216 fordefining the Y-axis (an axis extending in a direction perpendicular tothe conveying direction d) of the robot 12 is supported on the X-axisrobot arm 214 so as to be movable along the X-axis.

A robot arm (or hand) 218 for defining the Z-axis (axis extending alongthe vertical direction) of the robot 12 is provided to the side surfaceof the Y-axis robot arm 216 on the side of the feeding system. The robothand 218 is movable along the vertical direction, i.e., the Z-axis, andis also movable along the Y-axis and rotatable along the Z-axis.

More specifically, a servo motor M_(R1) for moving the Y-axis robot arm214 along the X-axis (conveying direction d) is arranged on the X-axisrobot arm 214. A servo motor M_(R2) for moving the robot hand 218 alongthe Y-axis (in a direction perpendicular to the conveying direction d),a servo motor M_(R3) for moving the hand 218 along the Z-axis (verticaldirection), and a servo motor M_(R4) for rotating the robot hand 218along the Z-axis are arranged on the Y-axis robot arm 218.

A finger 220 corresponding to one of parts x₁, x₂, x₃, . . . isdetachably mounted on the lower surface of the robot hand 218. Thefinger 220 is designed to grip the corresponding part x, and otherfingers 220 corresponding to retaining parts x₁, x₂, x₃, . . . areinterchangeably stocked in a finger station 222 provided to the frames212. Note that an assembling base 224 for assembling the part x grippedby the finger 220 is provided on the assembling stage 210. The I/Odevice 18 is arranged adjacent to one frame 212.

Operation of Robot

The assembling operation of a product using parts x in the robot 12 withthe above arrangement will be described below.

In an initial state, the robot hand 218 is positioned above the draw-outunit 154. From this initial state, when the pallet p retaining necessaryparts x is drawn out from the stocker 24 to the draw-out position, theservo motor M_(R3) is rotated from the time when it is detected that thepallet p is positioned at the draw-out position, so as to cause therobot hand 218 to be moved downward. Then, the gripping operation by thefinger 220 is executed. Upon completion of the gripping operation of thepart x, the servo motor M_(R3) is rotated in the opposite direction tomove the robot hand 218 upward, and the servo motors M_(R1) and M_(R2)are appropriately rotated to move the robot hand 218 above theassembling base 224.

The servo motor M_(R3) is rotated again to move the robot hand 218downward, and the assembling operation of the part x on the assemblingbase 224 is executed. Upon completion of the assembling operation, thegripping stale of the part x by the robot finger 220 is released, andthe servo motor M_(R3) is rotated in the reverse direction to move therobot hand 218 upward. Thereafter, the servo motors M_(R1) and M_(R2)are rotated to return the robot hand 218 to the above-mentioned initialposition. In this manner, a series of assembling operations regardingone of the parts x is completed.

During execution of the series of assembling operations, the pallet psubjected to the gripping operation of the parts x by the robot hand218, i.e., the pallet p which has completed feeding of the parts x tothe robot 12 is replaced with another pallet p which retains parts xnecessary for the next assembling process, until the robot hand 218 ismoved from the position above the pallet p to the assembling position,and is then returned to the position above the pallet p.

The time required for assembling one part x in the robot 12 is set to be2.6 sec, i.e., a total of 0.3 sec for the downward movement toward thepallet p, 0.2 sec for the gripping operation of the part x, 0.3 sec forthe upward movement from the pallet p, 0.5 sec for the movement to theposition above the assembling base 224, 0.3 sec for the downwardmovement toward the assembling base 224, 0.2 sec for the assemblingoperation at the assembling base 224, 0.3 sec for the upward movementfrom the assembling base 224, and 0.5 sec for the upward movement to theposition above the pallet p.

The draw-out/draw-in operation of the pallet p must be performed untilthe robot hand 218 starting from the position above the pallet p afterit was moved upward from the pallet p is returned to the position abovethe pallet p during the operation time of the robot 12 described above.In other words, during a time interval wherein the robot hand 218 ismoved downward from the standby position located above the pallet p, itgrips the part x on the pallet p, and is then moved upward to theposition above the pallet p; the draw-out/draw-in operation of thepallet p is therefore inhibited, and must be performed for a timeinterval other than the above-mentioned interval. For this reason, themaximum time allowed for the draw-out/draw-in operation of the pallet isdefined as:

    0.5+0.3+0.2+0.3+0.5=1.8 sec

In other words, if the draw-out/draw-in operation of the pallet p iscompleted within 1.8 sec, the feeding operation of the next part x canbe achieved without interrupting the assembling operation of the robot12. For this reason, the operation time of the above-mentioned stocker24 is set so that the draw-out/draw-in operation of the pallet p can beexecuted within 1.8 sec.

OPERATION OF SYSTEM

A method of controlling the operation of the FAC system according tothis embodiment will be described hereinafter.

Arrangement of Control Unit

FIG. 18 shows the arrangement of modules of the control unit 16 (FIG. 2)for controlling the FAC system of this embodiment. As described above,the FAC system of this embodiment includes the robot, stocker, elevator,and buffer as major components. The components are moduled not only in astructural sense but also in a control sense. More specifically, thecontrol unit 16 has four microprocessor boards, i.e., a microprocessorboard for controlling the robot, a microprocessor board for controllingthe stocker, a microprocessor board for controlling the elevator, and amicroprocessor board for controlling the buffer. These microprocessorboards are coupled through a known multibus interface. The fourmicroprocessor boards are subjected to systematic management by a hostmanagement microprocessor board. The management microprocessor board isconnected to the I/O device 18 shown in FIG. 2 through an RS232interface. The management microprocessor board receives and designatesassembling environments (e.g., designation of parts retained in apallet, process order, and the like) from the I/O device 18 employing anormal personal computer.

Since the interior of the control unit 16 is moduled in units of controlobjects, as shown in FIG. 18, this FAC system can select from among theabove-mentioned modules in consideration of various set conditions ofenvironment, limitation, and the like. In addition, since the assemblingenvironments are input from the I/O device 18, the setting can bedesirably changed. This FAC system can reconstruct "flexible" systemenvironments as its name implies. This will be understood fromdescriptions of the control unit program for the basic arrangement ofthe FAC system, modifications of various arrangements of equipmentdeveloped from the basic arrangement, and modifications of the program.

Inputting of Assembling Environment

The technical principle of this FAC system is not limited tomanufacturing, but ultimately aims at selecting an article one by onefrom among a plurality of article groups (each article group includesarticles of an identical means) in accordance with a predeterminedorder, and then "feeding" the selected article toward a given point. Asthe articles are fed toward the given point, the articles in eacharticle group become short. Thus, the technical principle of this FACsystem is summarized as a "feeding" of new articles toward the one givenpoint without interruption of such feeding. An embodiment by which thetechnical principle of the present invention is applied includesautomatic assembly by means of a robot. Such operation of the FAC isdefined in a narrow sense and will be described below in detail. In theFAC system defined in the narrow sense, "feeding of articles"corresponds to "feeding of parts" to the robot by the stocker, and"supply of articles" corresponds to supply of new parts to the stackerby the buffer or elevator (including an unmanned vehicle, unmannedwarehouse, and the like). "Assembling environments" in the FAC system inthe narrow sense will be described below.

FIGS. 19A to 19C show display screens of the I/O device 18. The displayscreen is used when an operator inputs and changes various assemblingenvironments at a keyboard, and is also used to display the presentcontrol conditions along with transition of control.

The assembling environments of this FAC system are, e.g., pallet data,i.e., a part name of a given part, a shelf position S of a palletretaining the parts in the stacker, a total count T of parts which canbe retained in the pallet, a thickness H of the pallet, a program numberP for assembling and finishing the parts into a product by the robot, abar code B printed on a predetermined location of a pallet, a number Fof a finger which is attached to the robot hand so as to be used for thepart, and the like. This FAC system employs standard-sized pallets asshown in FIG. 3. Therefore, if a part is determined, the assemblingprogram P (e. g., screw fastening) of the part, and the specificationsof a pallet retaining the part are determined. Determination of thepallet, e.g. the thickness H, is to depend upon the total count T ofparts retained in the pallet, the height of the parts, and the like.

A table of parts to be used shown in FIG. 19A is prepared as follows.The operator inputs the total count T of the parts retained in a pallet,the thickness H of the pallet, the bar code B of the parts, the fingernumber F of the robot necessary for the assembly of the parts, and theprogram number P. The operator, observing the CRT display screen of theI/O device 18, functions independent of process orders. The processorder G and the stocker shelf position S are automatically input anddisplayed by a management module program (FIG. 18) functioning in placeof the operator when a process order table (to be described later) isinput. Since the remaining parts count Z changes along with the progressof this process, the latest updated Z is continually displayed. Duringthis process of inputting the parts table, an index number IDX isassigned to the parts. The parts can then be specified by the IDX numberrather than direct part names. The order input process of this FACsystem (FIG. 19B), thus further simplified.

In the case shown in FIG. 19A, for a pallet assigned with the partsindex number IDX "1", a parts name of "screw", the total count of partsretained in the pallet of "38", the pallet thickness of 50 mm, and aprogram number of "100" are input. For a pallet assigned with the partsindex number IDX "2", a parts name of "nut", the total count of partsretained in the pallet of "13", the pallet thickness of 25 mm, and aprogram number of "200" are input. For a pallet assigned with the partsindex number IDX "3", a parts name of "washer", the total count of partsretained in the pallet of "54", the pallet thickness of 100 mm, and aprogram number of "300" are input, and so on.

All the assembling environment data input by the operator are uniquelydetermined if the parts are determined. Since the parts necessary forassembling a given product are predetermined, pallets retaining thesenecessary parts, programs, fingers, and the like can be uniquelydetermined. Therefore, these data can be supplied from a centralproduction management computer system (FIG. 18) for simultaneouslycontrolling a plurality of FAC systems.

Data associated with parts are not enough to assemble a product from theparts, and it is important to know assembling order of the parts. Theoperator of this FAC system lists all the parts necessary for assemblinga variety of products in respective processes, and inputs them into theprocess order table (FIG. 19B) on the CRT The process order of "1", "2`,"3", . . . is assigned in the input order during its input process, andits number is given as a variable G. The operator inputs the parts indexnumber IDX to designate parts used in each process. The operator inputs,into the process order table, the shelf position S G! of the stocker, onwhich a pallet retaining the corresponding parts is to be placed. Morespecifically, identical parts may be used in different processes, andthe identical parts are retained in the same pallet. Therefore, thepallet on the same shelf is requested in the different processes. FIG.19B shows the process order table input in this manner.

The table in FIG. 19B is a display of the input data for parts, chosenfrom among a plurality of parts, necessary in assembling a specificproduct. There are up to 64 process orders available, i.e., process Nos.1 to 64 can be defined in this FAC system. The operator sequentiallyinputs the parts index numbers IDX and shelf positions S G! inaccordance with the process order while observing the display of theparts table shown in FIG. 19A. The program number P and parts name inthe process order table are inserted by the management program. When theprocess numbers G and the parts index numbers IDX are associated witheach other in this process order table, the process numbers G areassociated with pallets used for the corresponding processes by theparts table (FIG. 19A).

If one part/one process/one shelf is given, the process order isidentical to the shelf order S. If the parts are determined, themanagement program can detect the pallet thickness H based on the partstable. Thus, the management program, in place of the operator,calculates the shelf positions S G! and can input the calculatedpositions to the table even if the operator does not input S G!. Whenthe process order is intensively determined such that identical partsare taken out from a pallet on the given shelf even in differentprocesses, the operator must input S G! regarding the pallet thicknessH.

By another modification, the predetermined process order can be inputfrom the central production management computer system to the FAC systemthrough a communication line. This is possible because the process orderfor a given product is determined in advance by the production schedule,i.e., by the parts table input.

Variation Factors of Parts Feeding Efficiency

In the FAC system, the order of "feeding articles" (i.e., both theprocess order and the assembling order) has an extremely large influenceon "article supply" efficiency. Factors influencing the parts feedingand supply efficiency include the pallet thickness H G!, and the shelfpositions S G! of pallets. The pallet thickness restricts the totalnumber of pallets which can be stocked in the stocker 24. In this FACsystem, a product is assembled from a maximum number of parts determinedby the maximum number of pallets which can be stocked on the maximumnumber of shelves of the stocker. Therefore, when the number of palletsis restricted by the pallet thickness H, if identical parts are used ina plurality of processes in order to assemble a product, the identicalparts must be taken out from the given pallet to suppress the totalnumber of pallets. If parts in the given pallet are taken out in aplurality of different processes, the stocker 24 must be randomly movedupward or downward, and this leads to a decrease in a supply speed fromthe stocker 24 to the robot 12. In this manner, the process order G, thepallet thickness H, and the shelf position S G! determine the efficiencyof operation. Thus, the process order table must be carefully created inconsideration of the above-mentioned factors. Since the total count T G!is predetermined for each type of parts, generation frequency andgeneration order of empty pallets are influenced by the assembly andreplacing efficiency of empty pallets. The operation efficiency of theelevator and the buffer is therefore also influenced.

FIGS. 17A to 17E explain the influence of the total count T G! and theshelf position S G! on efficiency assuming that the pallet thickness Hremains constant. FIG. 17A shows the simplest case wherein pallets usedin the respective processes have the same T for different parts, and arestacked on the shelves in the process order (i.e., S G! is a forwardorder). In this case, the generation order of empty pallets correspondsto the process sequence order, and the stocker is uniformly movedupward.

Assuming that parts A and B are necessary for assembly, the assemblingorder must be A A B; 100 A parts can be retained in a pallet, and 50 Bparts can be retained in a pallet.

FIG. 17B shows a case wherein the parts A A B are taken out from palletsin processes 1 2 3. In this case, the stocker 24 is regularly movedupward, and the pallet replacing frequency is small. However, a largenumber of pallets are undesirably required.

FIG. 17C shows a case wherein parts A retained in a given pallet areused in processes 1 and 2. In this case, the stocker is moved regularly,the pallet replacing frequency is low, and there is no waste ofnecessary pallets. This is an ideal case sufficiently considering theparticular assembly, process order G, and pallet capacity T.

When the assembling order is A B A, if the process order and the shelfpositions are determined as shown in FIG. 17D, the number of shelves iswasteful, but the stocker is moved regularly. In the case of FIG. 17E,there is no waste of the number of pallets, and replacement of palletssuccessively occurs. However, the stocker 24 is abruptly vibrated in thevertical direction.

The influence of the assembling order, the process order G, the totalcount T G!, and the shelf position S G! on the parts feeding and supplyefficiency has been described with reference to detailed samples. ThisFAC system does not analyze factors which influence efficiency in themanner of the above elements, nor provide optimal assembling orders andparts feeding schedules. When the assembling schedule and the processorder are determined by an operator or the production managementcomputer, the FAC system can be flexibly applied to any process orderand schedule, and can most efficiently feed parts to the robot 12 andsupply parts to the stocker 24 within the range of the predeterminedschedule and order. More specifically, the process order G, the shelfposition S G!, and the like are processed as variables, as shown in FIG.21A, thus providing a flexible system.

As shown in the example of FIG. 17A, the process order table is inputsuch that the pallet stacking order in the stocker corresponds to theprocess order, so that the FAC system achieves "flexibility" withrespect to a change in the parts feeding efficiency to the robot. Inother words, this FAC system aims at maintaining continual assembly bythe robot 12. More specifically, the pallet stacking order in thestocker 24 is not always the process order, but can be an order ofpallets in which parts are used up to zero and which must be replaced.In a control operation for feeding parts to the robot 12 withoutinterfering with the operation of the robot 12 as the characteristicfeature of this system, the pallet stacking order corresponds to theprocess order in this embodiment in consideration of the followingfacts. That is, the total number of parts retained in a pallet variesdepending on parts and hence, pallet replacing timings do not alwaysfollow the stacking order in the stocker and cannot be easily predicted.A change in remaining parts count due to a parts picking error by therobot can be flexibly coped with, and inputting of the process order isergonomically suitable, as shown in FIG. 19B, and so on. Therefore, theprogram can be easily corrected so that the robot, stocker, elevator,and the like are optimally controlled in consideration of a case whereinthe pallet stacking order in the stocker does not correspond to theprocess order, as can be understood from the descriptions of controloperations of the basic arrangement of the embodiment and arrangementsof modifications.

A total of 20 stages of the shelves 156 of the stocker shown in FIG. 14are prepared in this embodiment, and are given as 1st, 2nd, . . . , 20thstages starting from the uppermost stage. As shown in FIGS. 14 and 20,the shelves are arranged at equal intervals (about 30 mm). Therefore,when pallets of three different thicknesses (25 mm, 50 mm, 100 mm) arestocked on the stocker, the 100-mm thick pallet occupies four shelves.In the case shown in FIG. 19A, a pallet retaining "screws" having thenumber IDX "1" in the first process is placed on the first shelf, apallet retaining "washers" having the number IDX "3" is placed on thethird shelf, and a pallet retaining "nuts" having the number IDX "2" inthe third process is placed on the seventh shelf. The shelf positions ofpallets (i.e., the stocker shelf position number S in FIG. 19A) arecalculated and determined by the management program in consideration ofthe pallet thicknesses or determined and input by the operator inconsideration of efficiency. These shelf positions are sequentiallydisplayed in the table shown in FIG. 19A.

In this manner, when the operator inputs predetermined minimum data inthe parts table and the process order table, the management programcalculates and displays the process order, the stocker shelf position S,and the like in the parts table. Thus, complicated and variousassembling environments can be set with high operability, and can beeasily altered by only changing the input data. Thus, process alterationand parts alteration can be flexibly coped with.

Other Display Elements

FIG. 19C shows pictorial symbol keys on the display screen of the I/Odevice. A "CONTINUOUS" key is used for instructing a normal continuousassembling/parts feeding operation mode. When the "CONTINUOUS" key isdepressed, a SINGLE flag in a memory (not shown) in the managementmicroprocessor (FIG. 18) is set to be "0". When the continuous operationmode is set and a "START" key then depressed, the system is continuouslyoperated until a "STOP" key is depressed or an abnormality occurs. A"SINGLE" key is used for designating a single operation mode. When the"SINGLE" key is depressed, the SINGLE flag is set to be "1", and asingle operation (the range of single operation varies depending onmodules) is executed each time the "START" key is depressed.

Variables Used in Control

FIG. 21A shows common variables (grobal variables) which can be commonlyused (accessed) by the microprocessors of the respective modules. Thesevariables are formatted in a two-dimensional array and indexed by anindex number G (process number). A replacement flag I G! is a flagindicating that a pallet of a process order G (S G!th shelf in thestocker from the uppermost shelf) is empty. Most of other commonvariables are the same as those shown in FIGS. 19A and 19B, and adetailed description thereof will be omitted.

FIG. 21B shows save areas of process numbers (E₁, E₂, D₁, D₂) in orderto queue preparation instructions of pallets to be replaced (issued tothe elevator and buffer when the remaining parts count Z in each palletbecomes 1) sent from the robot 12 to the elevator 26 and buffer 22. Ascan be seen from FIG. 21B, the number of queues is 2. This is because,in consideration of the mechanical speed (e.g., motor speed) of modulesused in this embodiment, three or more queues will not be generated evenin the worst case. Of course, since the mechanical speed variesdepending on devices to be used, the number of queues can be increasedto be 3 or more. The use of queues in this embodiment will be describedlater.

Vertical Movement Ranges of Modules

The vertical movement ranges of modules will be described with referenceto FIG. 22.

In the buffer, the buffer base 52 receives a stack of pallets from theunmanned vehicle 20 at a 900-mm high position above a floor. A positionat which the first separation pawls hook a pallet stacked immediatelyabove a pallet to be separated (to be referred to as a temporary storingposition hereinafter) is 1,410 mm high above the floor. A position atwhich the second separation pawls hook the pallet to be separated (to bereferred to as a "separation position" hereinafter) is 1,300 mm highabove the floor. The temporary storing position and the separationposition are nominal positions, and the thickness of a pallet has anallowance. Thus, vertical movement amount control of the bufferregarding the allowance is performed as will be described later (FIG.25B). The lowermost position of the buffer base 52 is 500 mm high abovethe floor. This position is given as a teaching origin of buffermovement control. A maximum number of pallets to be stacked on thebuffer base is set in consideration of pallet thickness and the like sothat the uppermost pallet does not exceed a 2,225-mm high position fromthe floor when a plurality of pallets are stacked on the buffer base andthe buffer base 52 is moved upward to the temporary storing position.

The unloading mechanism 76 is set at a 350-mm high position from thefloor. As described above, the buffer base can be moved downward to a500-mm high position from the floor as its lowermost position. Thebuffer base is moved upward during unloading so as not to interfere withunloading of empty pallets in a state wherein empty pallets are fullystacked on the unloading mechanism 76.

The vertical movement range of the elevator 26 will be described below.The uppermost position of the elevator 26 corresponds to the separationposition at which the pallet filled with parts hooked by the secondseparation pawls matches the slide guides 122 (to be referred to as a"pallet take-out position"). The pallet take-out position is given as ateaching position of elevator control. With this setting, the strokerange of the elevator is 800 mm.

The movement range of the stocker 24 will be described below. Asdescribed above, the stocker has 20 stages of shelves at 30-mmintervals. Therefore, the height of the stocker 24 is 600 (=30×20) mm.The 20th shelf position when a pallet on the 1st shelf is drawn out tothe draw-out unit 154 is the lowermost position of the stocker. Thisposition is given as a teaching origin, and is set to be 300 mm highabove the floor.

The origin of the vertical movement of robot teaching is 1,225 high(900+175+150) mm high above the floor. The finger of the robot handgrips one part from a pallet on the draw-out unit 154, moves the partupward, horizontally moves the part to the assembling position, and thenmoves the part downward.

Summary of Pallet Replacing Operation

A state will be described with reference to FIG. 22B wherein one palletfilled with parts is taken out from, the buffer 22 by the elevator 26and is replaced with an empty pallet in the stocker 24.

When the number of parts in a pallet is reduced to one, the robot 12instructs the buffer 22 to prepare for separation from the pallet andinstructs the elevator 26 to be moved to the separation position. Thepallet separated at the separation position (this position is a fixedposition) by the buffer 22 waits for the take-out operation by theelevator 26. When the elevator 26 is moved to the separation position(take-out position) and takes the pallet in the elevator body, theelevator is moved downward to a position to match with a pallet whichwill become empty soon (or has already become empty; a pallet which isnormally located immediately above a pallet which is drawn out onto thedraw-out unit 154 to the robot) in the stocker 24. The elevator 26 thenwaits for the next operation. This standby position varies depending onthe process order and shelf position S G!. However, when the pallets arealigned in the process order from the uppermost shelf, this standbyposition is a position indicated by a solid line 230, as shown in FIG.22B. In this manner, the empty pallet replacement preparation of theelevator is completed.

After a pallet retaining only one part is drawn out again from thestocker body to the draw-out unit 154 and the last part is gripped bythe robot 12, the remaining parts count in the pallet becomes "0". Then,pallet replacement between the stocker 24 and the elevator 26 isstarted. More specifically, the elevator draws the empty pallet in itslower portion in the standby position state 230 described above.Thereafter, the elevator is moved downward by one stage, and pushes outa pallet filled with parts to an empty stocker shelf. This push-outstate position is indicated by a broken line 232 in FIG. 22B.Thereafter, the elevator is further moved downward, and stacks the emptypallet on she unloading mechanism 76. Thus, replacement of the emptypallet is completed.

Detailed Description of Each Module Control

The schematic operation of the modules of the FAC system has beendescribed. A detailed control operation of the modules will be describedwith reference to FIG. 23A and subsequent drawings. Note that as hasbeen described above, this control program has a complicatedarchitecture since it can flexibly cope with cases illustrated in FIGS.17A to 17E. The following description of the module operation will bemade in consideration of a typical arrangement of assembling order,process order, and pallet stacking order. A detailed description of theinitial state of each module under the control of the correspondingmodule in a transfer process will be described as needed. The initialstate is as follows:

1: Pallets having the same thickness are stocked in all the shelves(i.e., 20 shelves) in the stocker, and the numbers of parts retained inpallets are different from each other.

2: The processes follow the shelf order, and one process uses one partin one pallet. More specifically the total number M of processes isequal to the total number of shelves of the stocker, i.e., 20.

3: Necessary supplementary pallets are stacked in advance on the bufferbase 52.

The arrangement with the above initial state is called a "simplifiedarrangement" for the sake of simplicity. The operations of the modulesstarting from this "simplified arrangement" are as follows:

1: The robot 12 performs a one part/one process assembling operationfrom each pallet.

2: The stocker draws out a pallet to the draw-out unit 154 while beingsequentially moved upward from the 1st shelf to the 20th shelf, andafter a pallet on the 20th shelf is drawn out to the draw-out unit 154,the entire stocker is moved downward, so that a pallet on the 1st shelfis drawn out again.

3: In the elevator and buffer, since the remaining parts counts Z ofpallets become 1 or 0 at different timings, the empty pallet replacingrequests are not always generated in the same order as the shelf orderof the stocker.

A description will be made beginning with the assembling operation bythe robot.

CONTROL OF ROBOT AND STOCKER Until Remaining Parts Count Becomes 1

Robot control is made in accordance with a program shown in the flowcharts of FIGS. 23A and 23B. Stocker control is made in accordance witha program shown in the flow charts of FIGS. 24A and 24B. Descriptions ofthese two modules are made together since the elevator, buffer, and thelike are not operated until the remaining parts count Z in some palletin the stocker becomes "1".

As has been described above, when the "START" key of the I/O device 18is depressed, the program of the management microprocessor (See FIG. 18)starts programs of the modules. The microprocessor of the robot moduleinitializes the process number index G to be "1" in step S8. The processnumber G="1" means that the robot requests a part having the processnumber "1", and hence means that a pallet on an S 1!st pallet of thestocker is requested to the stocker. In step S10, the state of theSINGLE flag (FIG. 19C) is checked. If the SINGLE mode is set, the flowadvances from step S10 to step S12. Only when the "START" key isdepressed, is the following control operation executed to perform asingle operation. In the following, continuous operation will bedescribed.

In step S14, the stocker is started. Instructions to other modules areissued through the above-mentioned multibus. After the stocker isstarted, the robot waits until the pallet of S G! in the stocker isdrawn out to the draw-out unit 154 (i.e., completion of palletpreparation).

Once the stocker in waiting detects a start instruction from the robot12 in step S60, the flow advances to step S62 to check if some pallethas already been drawn out onto the draw-out unit 154. This check ismade by a sensor (not shown) on the draw-out unit 154. The checkingoperation is performed both after the stocker is stopped and restartedfor any reason, and in the SINGLE mode. Therefore, if the pallet hasalready been drawn out to the draw-out unit 154, the flow advances tostep S64 to check if the drawn pallet (the type of pallet can bedetected based on the variable L) is one having process number G=1requested by the robot 12. If the pallet requested by the robot 12 isdetected, since a pallet need not be drawn out, the flow advances tostep S84, and a pallet preparation completion message is sent to therobot through the multibus. If it is determined in step S64 that thedrawn pallet is not one for the process G (S G!th shelf) requested bythe robot, the pallet is returned to the stocker in step S66. Theoperations of the air cylinder C_(S4) and the motor M_(S2) for returningthe pallet into the stocker have already been explained, and a detaileddescription thereof will be omitted.

If it is determined in step S62 that no pallet is drawn out or if thealready drawn pallet is returned in step S66, the flow advances to stepS68. The process number of the pallet requested by the robot is storedin the variable L. The variable G indicating the pallet requested by therobot is stored in the variable L by the stocker 24 since the robot andstocker can basically perform independent parallel operations whilesometimes taking synchronization.

The flow advances to step S70 to calculate the rotating degree requiredby motor M_(S1) for moving the stocker in the vertical direction tomatch the pallet requested by the robot with the draw-out unit 154. Themodule learns in advance the origin of the shelves of the stocker(300-mm high position from the floor in FIG. 22A), as shown in FIG. 20.Therefore, since the pallet for the process G (=L=1) is stocked in theshelf having the stocker shelf number S L! indexed by the value of L, SL! of L=1 is indexed from variables S L! shown in FIG. 21A, and ateaching point TP S L!! having the indexed value as an index number issearched from the teaching points shown in FIG. 20. The detected valueis given as a moving degree STP of the servo motor. That is,

    STP=TP S L!!

In step S72, the stocker is moved according to the moving degree. Whenthe servo motor M_(S1) is rotated to the STP position, the shelf storingthe pallet requested by the robot 12 has reached the draw-out position.A CH flag in step S74 indicates that the replacing request from therobot has already been issued. If G=L=1, the CH flag is reset since areplacement necessary state is not yet generated. Thus, the flowadvances to step S78. In steps S78 and S80, the lid of the correspondingpallet is opened, and the pallet with the open lid is drawn out to thedraw-out unit 154 under the above-mentioned control. When the palletabuts against the stopper 176 of the draw-out unit 154, a messageindicating that the pallet has completed preparation of the draw-outunit 154 is issued to the robot 12 in step S84. The stocker waits for apredetermined message from the robot 12.

When the robot 12 which waits for the preparation completion messagefrom the stocker 24 in step S16 (FIG. 23A) receives this message, theflow advances to step S18. In step S18, the robot 12 is moved to aposition above a part in order to pick up the part in the pallet placedon the draw-out unit 154, and is then moved downward to pick the part.In step S20, the remaining parts count Z G! of the parts for the processnumber G is decreased by one. It is then checked in step S22 if theremaining parts count Z has become "1". If the remaining parts count ZG! is larger than 1, it is checked in step S28 if the finger of therobot can pick the part. Unsuccessful picking of the part occurs when apart is not inserted in the corresponding location in the pallet or inthe case wherein the finger fails to grip the part. In this case, are-picking operation is performed in step S18 until the desired part canbe normally gripped or the remaining parts count becomes 1. If it isdetermined that the part can be normally picked, a picking completionmessage is sent back to the stocker 24 in step S32.

When the stocker 24 receives both a message indicating that the robot 12is in operation and a message indicating picking completion, the flowadvances in the order of steps S86, S88, and S90 to return the pallet onthe draw-out unit 154 into the stocker. In step S92, the CH flag ischecked. Since this flag is reset, the flow advances to step S100. Instep S100, I L! is a flag indicating that the remaining parts count Z inan Lth pallet detected by the robot becomes zero and a replacing requestis issued from the robot. Thus, this flag is reset at this time.Therefore, the flow advances to step S118 to increase L by one. That is,

    L=L+1

From step S118 to step S126, i.e., while the robot 12 assembles the partpicked in step S18 (FIG. 23A), the stocker 24 prepares for the nextpallet (part) on the draw-out unit 154. More specifically, it is checkedin step S120 if the present process is the final process. If it isdetermined in step S120 that the present process is not the finalprocess (when L=20 since the total number of processes is 20 in theabove-mentioned "simplified arrangement"), the flow advances to stepS126 to calculate the degree of movement required to move a shelf (L hasalready been incremented by one in step S118) to the draw-out unit 154position. The shelf to be moved is of a pallet next to the pallet fromwhich the part was picked up by the robot. In control steps S128 andS130, every depression of the "START" key in the SINGLE mode results inmovement of the stocker. The flow returns from step S130 to step S72 inFIG. 24A. Then, the data STP calculated in step S126 is sent to themotor M_(S1) to match the next shelf with the draw-out unit 154position. The above-mentioned control operations are repeated until theremaining parts count Z G! in some pallet becomes 1. The stocker controlprogram shown in FIG. 24B is programmed based on the assumption that allthe processes of assembly require parts. However, in practice, someprocesses, e.g., a finger exchanging process, do not require parts. Inthis case, the shelf movement of the stocker (step S126) need not beperformed. Thus, a flag for discriminating if a process requires parts(or parts indexes are represented by alphabets) can be set. Before stepS126, the value of this flag is checked. If it is determined that theprocess does not require parts, the flow does not advance to step S126but returns to step S118 so as to advance the process.

When Remaining Parts Count Has Reached 1

The remaining parts count Z G! of the shelf S G! then becomes 1 in agiven process G. More specifically, When one part is picked up from thepallet having the remaining parts count of 2 in step S18, since theremaining parts count becomes 1, the flow advances from step S22 to stepS24. The process number G is saved in the process number variables E andD to be used in the elevator and buffer control programs. In step S26,the elevator and buffer are instructed to start preparation of a newpallet since the empty pallet will soon be detected. The replacementpreparation instruction is stored in the queue area described above. Ifthe elevator and buffer are not busy in the previous replacementpreparation operation, they extract the queue and start the replacementpreparation operation.

After the replacement preparation instruction is issued to the bufferand elevator, the robot maintains the picking operation as long as amessage indicating that the pallet is drawn out from the stocker to thedraw-out unit 154 position is detected in step S16.

In the control operation of this embodiment, the stocker 24 stops itsoperation when the robot 12 detects that the remaining parts count Z ofthe pallet in a given process G (=L) becomes zero. A message indicatingsuch is sent to the stocker (by means of I L!). The stocker draws out apallet for the next process G+1 (=L+1) to the draw-out unit 154. Therobot picks up a part in the pallet of G+1. The replacing operation ofthe pallet whose remaining parts count is zero as detected in theprocess G, is not yet completed (step S94). More specifically, thestocker waits until the replacing operation is completed. Since a palletfor a process G+1 next to the process G in which the remaining partscount Z G! becomes zero still retains parts, replacement of the emptypallet in the process L (=G) can be performed parallel to the partsassembly in the process (G+1) by the robot.

PALLET REPLACEMENT Pallet Separation by Buffer

FIG. 25A shows variables used in the buffer control program. Morespecifically, these variables include a stage number of the uppermostpallet placed on the buffer base, a read data storage area B by the barcode reader, the pallet height data in units of stages, parts names, andthe like. The stage number of the uppermost pallet is used to indicate apresently valid portion of these variables since the data of a taken-outpallet is deleted along with the take-out operation of pallets from thebuffer by the elevator. As will be described later, when this FAC systemrequests a necessary pallet to the unmanned warehouse through theproduction management computer, and when the pallet is transferred fromthe unmanned vehicle to the buffer without a manual operation, thesedata are supplied from the system (the program of the managementmicroprocessor shown in FIG. 18) to the buffer. In contrast, when thepallets are manually stacked on the buffer base 52, the above-mentioneddata are input from the I/O device 18.

The robot issues a replacement preparation instruction to the bufferthrough a queue in step S26 (FIG. 23A). A process number correspondingto a pallet necessary for the replacement preparation is saved in thevariable D in the queue in step S24. When the buffer receives thereplacement preparation instruction in step S150, the flow advances tostep S152, and the parts name (or parts index IDX) of the pallet to bereplaced is searched from the variable table shown in FIG. 21A based onthe process number D supplied from the robot. The parts name (partsindex IDX) is then searched from the table shown in FIG. 25A to detectthe position of the shelf on which the parts pallet to be replaced isstacked. In step S154 a distance (given by l) from the buffer base 52 tothis pallet is calculated. The distance is obtained by summing thethicknesses (detected from the table shown in FIG. 25A) of all thepallets up to the pallet of this shelf, and a distance (given by m) fromthe floor to the lower end of the present position of the buffer base isthen detected. A moving distance of the pallet to be replaced to theseparation position is calculated based on the m and l using thefollowing formula, in step S156:

    {1410-(m+l)}mm

In step S158, the buffer base 52 is vertically moved by the calculatedmoving distance. The moving distance can be easily understood withreference to FIG. 7A wherein the third pallet from the uppermost palletis to be replaced.

In step S160, the sensing state of the sensor 80 is checked. If thesensor 80 is OFF, the buffer base 52 is moved upward until the sensor 80is turned on. If the sensor 80 is ON in step S160, the buffer base 52 ismoved downward until this sensor is turned off. The reason why suchcontrol operation is performed in association with an allowance of thepallet thickness has already been described with reference to FIGS. 8Ato 8E, and a detailed description thereof will be omitted.

When a desired pallet has reached the separation position, the bar codeprinted on the pallet is read by the bar code reader 74 for the purposeof confirmation. In step S168, the read data R is compared with B D! inthe variable table (FIG. 21A). If noncoincidence is found, the palletmoved to the separation position is immediately above the pallet to bereplaced. Thus, the flow advances to step S170, and the thickness of thecorresponding pallet is obtained from the table shown in FIG. 25A. Instep S172, the buffer base 52 is moved upward by a distancecorresponding to the obtained thickness, so that the desired pallet ismoved to the separation position. In steps S174 and S176, the bar codereading operation is performed again to check the pallet. The flowadvances from step S168 or S176 to step S178, and the first separationpawls 66 are biased. In step S180, the buffer base is moved downward bya predetermined distance L₁ (a distance larger than the maximum palletthickness; 94 mm in FIG. 22A) to achieve a state shows in FIG. 7C. Instep S182, the second separation pawls 68 are biased. In step S184, thebuffer base is further moved downward by a predetermined distance L₂,thereby separating the pallet as shown in FIG. 7D. In step S186, amessage indicating completion of the pallet separation is sent to theelevator 26. In step S188, control stands by until the elevator draws inthe separated pallet in the elevator body.

Pallet Take-out Operation by Elevator

When an empty pallet need not be replaced, the elevator need not beoperated. In the replacing operation, an operation for taking the palletfilled with parts separated by the buffer into the elevator body mustfirst be performed. Therefore, assuming that the normal standby positionof the elevator is a position matching the separation position of thebuffer (origin of the elevator shown in FIG. 22A), when a palletpreparation instruction is issued from the robot and the separationoperation is immediately completed in the buffer, the take-in operationof the pallet into the elevator body can be started without firstrequiring time for movement. In elevator control of this embodiment, asshown in step S200 of FIG. 26A, the elevator body standby position ofthe elevator coincides with the separation position of the buffer.

Independent of the operation of the buffer, the robot issues areplacement preparation instruction to the elevator through a queue(FIG. 21B) in step S26 (FIG. 23A). The process number G corresponding tothe pallet necessary for this replacement preparation is saved in thevariable E in the queue in step S24. When the elevator receives thereplacement preparation instruction, the flow advances from step S204 tostep S206, and the elevator waits for the pallet separation completionmessage at the separation position by the buffer.

As described above, the buffer has issued the separation completionmessage to the elevator in step S186, and thereafter, waits that theelevator takes in the pallet, in step S188.

The elevator receiving the message performs the pallet draw-outoperation in step S208. In the draw-out operation, as described abovewith reference to FIGS. 13A to 13D, the motor M_(E2) of the elevator isrotated in the direction of the arrow A to move the first hooks 108 tothe position for hooking the pallet. Then, the air cylinders C_(E1) aredriven to cause the hooks 108 to be engaged with the pallet. The motorM_(E2) is then rotated in the direction of the arrow B to take thepallet into the elevating frame from the buffer. Upon completion of thedraw-out operation of the pallet from the buffer, a message soindicating is sent back to the buffer in step S210. The flow advances tostep S212 and the subsequent steps.

Stacking of Upper and Lower Pallets by Buffer

The buffer having received the message releases the second separationpawls 68 in steps S188 to S190. In step S192, the buffer moves thebuffer base 52 upward by a distance expressed as:

    L.sub.1 +L.sub.2 +H D!

Thus, the pallets which are vertically separated are stacked again. Thefirst separation pawls 66 are retracted in step S196, and the flowreturns to step S150 to wait for the next pallet preparation instructionfrom the robot. The instruction standby position from the robot in stepS150 is not limited to a position attained by upward movement of (L₁ +L₂+H D!) in step S192 but can be an origin (a 500-mm high position fromthe floor in FIG. 22A). If the numbers of parts retained in the palletsdiffer depending on pallets like in this embodiment, timings ofdetecting a remaining parts count=1 become random (although they can bepredicted).

Elevator Replacement Standby Position

Prior to a description of movement control to the replacing position, amethod of determining the replacing position will be described below.This FAC system aims at achieving supply of new parts withoutinterrupting the robot operation and easy alteration of assemblingprocedures. From this point of view, the method of determining thereplacing position is an important factor.

In the "simplified arrangement" described above, a pallet from which apart was picked up by the robot is moved upward. Regarding that theshelves of the stocker are always fed upward, assume that efficiency isto be improved by replacing a pallet with the remaining parts count Z=0while the robot uses another pallet. In this case, in FIG. 27A, when thepallet is drawn out to the draw-out unit 154, the pallet replacementpreparation instruction is issued to the elevator and buffer. Since theremaining parts count of the pallet becomes 1 when the correspondingpallet is drawn out to the draw-out unit 154 next, the pallet with theremaining parts count=0 is moved upward, and a new pallet can be mostlyefficiently replaced with an empty pallet while the lower pallet isdrawn out to the draw-out unit 154. More specifically, in FIG. 27A, theelevator need only replace pallets while the pallet with the remainingparts count=0 is located at the illustrated position. Thus, a downwardmovement distance of the elevator to the illustrated replacing positionwill be examined below.

In FIG. 27A, the vertical positions of the second separation pawls 68 ofthe buffer and the slide guides 122 of the elevator are matched witheach other, thus allowing a smooth draw-out operation. Reference numeral134 denotes a plate for drawing out an empty pallet from the shelf ofthe stocker to be slid therealong. A distance between the slide platesis fixed. Therefore, the position of each slide plate 134 when theseparated pallet is taken into the frame has a fixed distance from thefloor (see FIG. 22A). When the elevator is moved such that the emptypallet can be placed on the slide plates 134, since the shelf number Son which the pallet to be replaced is placed can be easily detected, adistance to the teaching position of that shelf corresponds to a movingdistance of the elevator. Note that FIG. 27A illustrates a state whereina pallet to be drawn out from the buffer by the elevator is apt to bereplaced with a pallet with the remaining parts count=0, for the sake ofdescriptive convenience. In the "simplified arrangement", when a palletis to be drawn out from the buffer to the elevator, the pallet with theremaining parts count=0 should be one with the remaining parts count=1as a cause of the replacement preparation instruction.

A case will be examined when the process order does not correspond tothe shelf positions of the pallets. In this case, the processes Gprogress in an order of 1, 2, 3, . . . , and the stocker is verticallymoved in accordance with S G!. FIG. 27B illustrates a case wherein apallet for a process L (=G) has Z G!=1. The elevator then startsreplacement preparation together with the buffer, receives a new palletfrom the buffer at the separation position, and then is about to move tothe standby position of the elevator. In this case, since the robot hasalready requested a pallet of the next process (L+1), the pallet of theprocess L+1 has already been drawn out onto the draw-out unit 154 of thestocker. In this case, the pallet of the process L has been moved to theposition illustrated in FIG. 27C. It should be noted that when theprocess G is circulated from 1 to its maximum value, it changes again inthe same order as that starting from 1. More specifically, the positionof a pallet (placed on a shelf S L!) whose remaining parts count became1 in a process L in a given cycle when a pallet placed on a shelf S L+1!is drawn out to the draw-out unit 154 in the next process L+1 is equalto the position, when the pallet placed on the shelf S L+1! is drawn outto the draw-out unit 154 in the process L+1, of the pallet whoseremaining parts count became zero from 1 when the processes werecirculated and the process L returned in the next cycle. Therefore, thereplacement standby position when the remaining parts count becomes zerocan be predicted when the remaining parts count becomes 1, without anycontradiction.

From this point of view, a calculation of the replacement standbyposition will be described with reference to FIG. 27D. The initialposition of the crocker is illustrated in the left portion of FIG. 27D.More specifically, a distance t_(O) from the floor of the 20th shelf atthe draw-out position of the 1st shelf is 300 mm, as can be seen fromFIG. 22A. When the remaining parts count of a pallet on a shelf S L!becomes 1 in a given process L and a pallet on a shelf S L+1! is drawnout to the draw-out unit 154 in a process L+1, the pallet of the processL has been moved to the position illustrated in FIG. 27D. When thisstate is viewed from the elevator, this is equivalent to calculation ofthe position of a pallet on a shelf S E! when a pallet on a shelf S E+1!is located at the draw-out position, as shown in FIG. 27D. Morespecifically, from FIG. 27D, in consideration of the intershelfdistance=30 mm and the total number of shelves=20, the replacementstandby position is expressed as:

    30×{20+S E+1!-S E!)+t.sub.0

In this manner, the replacement of the standby position by the elevatoris determined.

In FIG. 27C, when a pallet of the process L+1 is drawn out to thedraw-out unit 154 and the remaining parts count Z L+1!=1 is detected, asecond replacement preparation instruction is issued in step S26 of therobot control, and is queued, as has been described above.

Movement to Standby Position

In step S212 in the elevator control program, it is checked if a shelfposition S E! in the stocker of a pallet with the remaining partscount=1 of a process E is the last shelf on which a pallet is stacked inthe stocker. If pallets are stacked on all the 20 shelves of the stockerof this embodiment, the last shelf is the 20th shelf. This decision mustbe made since any shelf is not present below the last shelf or if any, apallet thereon may not belong to the process (i.e., no pallet ispresent). In this embodiment, an algorithm of determining a palletreplacement position is altered depending on the last shelf or not. Thisdecision can be achieved as follows. That is, the value of S E! iscompared with all the values of shelf position data S (FIG. 21A) in thevariable table to check if the S E! has a maximum value.

A description of control when the last shelf is reached will bedescribed later. If it is determined that S E! does not corresponds tothe last shelf, the flow advances to step S214, and the above-mentionedreplacement position is calculated as follows:

    30×{20+S  E+1!-S  E!}+t.sub.0

When the replacement position is determined as described above, theelevator is moved in step S216. The elevator waits for the replacementinstruction from the stocker at this replacement standby position.

In other words, the robot detects a pallet with the remaining partscount=1 and sends the replacement preparation instruction to the bufferand elevator based on the detection result, the elevator receives a newpallet from the buffer in response to the instruction, and the elevatorhaving the new pallet is moved to the replacement standby position.

Detection of Remaining Parts Count 0

When the robot successively detects pallets with the remaining partscount=1 in the successive processes, it can output up to two replacementpreparation instructions, as has been described with reference to FIG.21B. That is, before this detection, the robot sequentially picks upparts from the stocker to assemble a product independently of theoperations of the buffer and elevator. In other words, until a new thirdpallet with the remaining parts count=1 is detected, at least the firstpallet whose remaining parts count becomes 1 must use up parts first.

The remaining parts count=0 is detected in step S34 (FIG. 23A). If theremaining parts count=0 is detected, the flag I G! is set to be 1 instep S36, and the next control operation is continued. Morespecifically, the robot expects that the corresponding pallet bereplaced in the stocker by the elevator until the process requesting thesame parts retained in the empty pallet comes after one cycle of theprocesses. When the pallet is not replaced in any event, the robot isinterrupted to wait for the preparation completion instruction from thestocker in step S16.

Pallet Replacement

The stocker detects I G!=1 set by the robot when step S100 (FIG. 24B) isreached. The state of the stocker in the above-mentioned "simplifiedarrangement" when this flag is detected will be described with referenceto FIG. 24C.

FIG. 24C illustrates a state wherein 3, 2, 3, 4, and 5 parks areinitially retained in pallets on five shelves of the stocker,respectively, from the uppermost pallet.

After a cycle of assembly (all the processes) by the robot from thisstate, the numbers of parts retained in the pallets are reduced to (2,1, 2, 3, and 5), respectively. When the second pallet is drawn to thedraw-out unit 154, the pallet replacement preparation instruction issent to the elevator and buffer, as a matter of course. When a part ispicked up from the first pallet in the next cycle, since the number ofparts left in this pallet also becomes 1, this pallet preparationinstruction is queued. When a part is picked up from the second pallet,the number of parts retained in this pallet becomes 0, and the I G! flagfor the second pallet is set to be 1 at this time.

This operation will be described in more detail. The stocker draws outthe second pallet onto the draw-out unit 154 in order to pick up thelast part from this pallet, in step S82 (FIG. 24A). The flow advancesfrom step S82 step S84, and a pallet draw-out completion message is sentto the robot. Upon reception of this message, the robot sets the I G!flag in step S16 step S18, . . . , step S36.

In the stocker, the flow advances to step S84 step S86 step S88 step S90step S92 step S100, and I L!=1 is detected. In other words, when thepallet with the remaining parts count=1 is drawn out to the draw-outunit 154, the robot picks up the last part therefrom, and the stockerreturns the pallet with the remaining parts count=0 therein, the stockerdetects I L!=1.

When I L!=1 is detected in step S100, the flow advances to step S102,and the CH flag is set to be "1". The reason why only the CH flag is setand the replacing operation is not immediately performed is as follows.At this time, a pallet with the remaining parts count z=0 is present onthe stocker shelf at the draw-out position to the robot, and the partsare still retained in the pallet for the next process. Therefore, thestocker temporarily loads the pallet of the next process to the draw-outposition to the robot so as not to interfere with the operation of therobot. Thereafter, the replacement request can be issued. The flowadvances from step S102 to step S104, and it is checked if the S L! hasa maximum value, i.e., the stocker shelf of a pallet with the remainingparts count=0 is the last shelf in the stocker in accordance with thesame reason as that in step S212 of the elevator described above.

If the last shelf is not detected, the flow advances to step S106, andthe process number L having the remaining parts count=0 is temporarilysaved in a register P. This is to hold the process number L with noparts in order to load a pallet of the next process (L+1) to thedraw-out position for the robot so that the stocker does not interferewith the operation of the robot. Thereafter, the process number isincremented in steps S118 to S130, and in step S72, the stocker is movedto the shelf position of the next process. In step S74, since the CHflag has already been set, a replacement request of the empty palletwith a new pallet is sent to the elevator in step S76.

If the elevator having a new pallet has already reached the replacementstandby position at this time, pallet replacement must be immediatelystarted by the elevator independently of stocker control. As bas beendescribed above, pallet replacement preparation was started when theremaining parts count became 1. Therefore, when the replacement requestis sent to the elevator in step S76, the elevator is expected to havereached the replacing position. Refer to FIG. 27E for this point.

After the replacement request is sent to the elevator, in the stockercontrol, a pallet of a process next to the pallet with the remainingparts count=0 is drawn out to the draw-out unit 154 in steps S78 to S82.In steps S84 to S92 step S94, the robot is caused to assemble the partfrom the pallet of the next process. In step S94, the pallet replacementcompletion message is waited for. In this manner, empty palletreplacement is performed so as not to interfere with the robot operationas much as possible.

The description of the elevator control program will be made again. Whenthe elevator which has been waiting for the replacement request from thestocker in step S218 receives the request, it performs the palletreplacing operation in step S220. The detailed control operation of stepS220 is shown in steps S240 to S256 in FIG. 26B. However, since theoperation sequence under this control follows FIGS. 13A to 13G, adescription thereof will not be repeated. When FIGS. 27E and 27F areassociated with the control operation shown in FIG. 26B, FIG. 27Ecorresponds to steps S240 to S246, and FIG. 27F corresponds to stepsS248 to S256. Note that denotes a thickness of the flange 38 of thepallet shown in FIG. 4, and is 12 mm in this embodiment.

When the elevator completes pallet replacement, it sends a replacementcompletion message to the stocker (step S222). When the stocker receivesthis message, the flow advances from step S94 to step S96, and theremaining parts count of a pallet to be replaced of a process P isinitialized. In step S98, the CH flag is reset, and the flag I P! isalso reset. The flow advances to step S100 S118, and the next processL=L+1 is performed. The flow then returns to step S120 . . . step S130step S72, and the above-mentioned operation is repeated.

Stacking of Empty Pallet

On the other hand, the elevator performs operation control for stackingthe empty pallet held below the elevator on the unloading mechanism 76.

More specifically, in step S226, a value obtained by subtracting theedge β of the pallet from the present pallet height H E! is added to theprevious stacking height Q of the empty pallets. More specifically, thedownward movement position is expressed as:

    Q+H E!-β

This can be understood from FIG. 28. The elevator is moved to thedownward movement position, and the air cylinders C_(E4) are released tostack the empty pallet. After the empty pallet is stacked, since thepallet is lowered by an amount corresponding to a stacking margin α(=7mm), the updated stacking position Q is expressed as:

    Q=Q+H E!-α

It is then checked in step S234 if the stacked empty pallet has reachedthe position of the sensor S₄ (shown below the elevator in FIG. 1) fordetecting interference with the elevator movement. If the empty pallethas reached the position, the unloading mechanism 76 is driven in stepS236 to convey the empty pallets to the unmanned vehicle position.

In this manner, empty pallet replacement is completed, and the partsfeeding operation to the robot and the parts supply operation to thestocker can be successively performed without interrupting the operationof the robot.

The basic operation control of this FAC system has been described. Thiscontrol program is variously contrived to improve efficiency.

Replacement of Final Shelf

One technique of improving efficiency is alteration of a controlsequence upon replacement of the final shelf. The stocker of this FACsystem has a total number of shelves as 20. Therefore, when pallets areplaced on the shelves in the process order starting from the uppermostshelf, no pallet is present below the 20th shelf. When all the palletsused for all the processes are placed on the shelves and do not fill thestocker, there is no pallet below the lowermost shelf. In this manner,when pallets are placed on the shelves in the process order startingfrom the uppermost shelf, if replacement of the final shelf is performedin accordance with determination of the replacement position describedabove, a shelf with no pallet is moved to the draw-out unit 154position, and an empty pallet is replaced at the replacement positionthereabove. However, the robot must interrupt assembly while waiting fordraw-out completion in step S16 until pallet replacement is completed.

In order to eliminate this drawback, steps S104 to S116 in FIG. 24B, andsteps S212 and S224 in FIG. 26A are provided. More specifically, ifthere is no need for pallet replacement at the final shelf position,replacement is performed at the draw-out position of the stocker(position of the slide plate 178 of the draw-out unit 154). In thiscase, as shown in FIG. 27G, the replacement standby position isexpressed as:

    30×S  E!+t.sub.0

Therefore, in the elevator, the flow advances to step S212 step S224,and the standby position is calculated based on the above formula. Theelevator is then moved to the draw-out position to wait for thereplacement request from the stocker in step S218.

In the stocker, if it is detected in step S100 that the replacement flagI L! is set, the CH flag is set in step S102. Then, the flow advances tostep S104 S108, and the stocker issues the replacement request to theelevator.

The subsequent control operation is the same as that in the replacementat a normal shelf position, and a detailed description thereof will beomitted.

When a pallet to be replaced is a final pallet, pallet replacement isperformed at the draw-out position of the stocker to the robot.Therefore, an unnecessary wait time can be eliminated. This operation isparticularly effective when pallets are placed on shelves in the processorder starting from the uppermost shelf.

QUEUING OF REPLACEMENT PREPARATION INSTRUCTION

Another technique for improving efficiency is queuing. The queuing isnecessary from the following background. More specifically, if theoperating speeds of the modules (e.g., the motor speed) can be set sothat a total time required for replacement preparation such as a timerequired for separating a pallet by the buffer, a movement time of theelevator to the replacement standby position, and the like becomesshorter than a time required for one process of assembly by the robot, aplurality of replacement preparation instructions (step S26) will not beissued from the robot to the buffer and elevator. However, the formertotal time may be longer than the latter. In this case, a plurality ofinstructions may be issued. In order to cope with this, the instructionsmust be queued. For example, when the total numbers of parts in thepallets are the same and the parts are used in the same manner in twosuccessive processes, the replacement preparation instructions maysometimes be successively issued. In particular, in the two successiveprocesses (these two processes are given by L and L+1 in the stocker),if shelf positions S L! and S L+1! are not succeeded, the stocker mustbe vertically moved, and it takes a long time to replace pallets. Inthis case, as shown in FIG. 21B, if the replacement preparationinstructions are queued, the robot operation will not be interrupted.This is because after a pallet is separated to perform a singlereplacement operation in the buffer and the separated pallet istransferred to the elevator, the next queued instruction can beimmediately fetched from the queue, and the next pallet separationoperation can be performed. In this embodiment, the number of queues isset to be two, but may be increased as needed.

INITIAL OPERATING STATE SETTING

The description of the control operation will be made under theassumption that the pallets are placed in the stocker. Initializationcontrol for inserting pallets to the stocker will be described withreference to FIG. 29. In this initialization, the robot and stocker arenot operated, and the buffer and elevator insert pallets in the shelvesof the stopped stocker.

In step S300, the buffer receives stacked pallets from the unmannedvehicle. In step S302, 1 is set in a counter n. In step S304, an nthpallet is moved to the separation position, and the pallet is separatedin step S306. In step S308, a separation completion message is sent tothe elevator. In step S310, the buffer waits for completion of thepallet draw-out operation by the elevator.

In step S352, the elevator is moved to the separation position as soonas the program is started. In step S354, the elevator waits for theseparation completion message from the buffer. Upon reception of thismessage, the elevator calculates the shelf position of the stocker inaccordance with the counter set by the buffer based on the followingequation:

    STP=TP  n!

The elevator is then moved to the calculated position. In step S358, theelevator pushes the pallet into the corresponding shelf. In step S360, amovement completion message is sent to the buffer, and the next palletis waited for in step S352.

When the buffer receives this message, it updates the counter n in stepS312. This updating operation is performed as follows. The necessarynumber of shelves of pallets presently placed on the stocker iscalculated from the thickness data of the pallets transferred from theunmanned vehicle, in step S300, and a shelf count in which the nextpallet is to be inserted is calculated. In step S314, it is checked ifpallets are left on the buffer base. If some pallets are left on thebase, the flow returns to step S300 to separate the next pallet.

In this manner, the initial operating state setting is completed.

DESCRIPTION OF MODIFICATIONS

The present invention is not limited to the arrangement of the aboveembodiment, and various changes and modifications may be made within thespirit and scope of the invention.

Modifications of the above-mentioned embodiment will be describedhereinafter in detail. In the following description, the same referencenumerals in the modifications denote the same parts as in thearrangement of the embodiment, and therefore, a detailed descriptionthereof will be omitted.

Description of First Modification

In the buffer 22 of the above-mentioned embodiment, the rob&t 12 detectsthat the remaining parts count x in the pallet p becomes 1. Thereafter,when the last part x is used in the assembly and the correspondingpallet becomes empty, the empty pallet p' is replaced with a new palletp filled with parts x without interfering with the operation of therobot 12. For this purpose, when the remaining parts count=1 isdetected, the pallet p filled with the same parts x as those in thepallet with the remaining parts count=1 is separated from other palletsp in the buffer 22 through the separation mechanism 64 in order to betaken from the buffer 22.

However, the present invention is not limited to the above arrangement.In place of the separation mechanism 64, the buffer 22 may comprise astack separating mechanism 250 for simultaneously separating a pluralityof pallets p₁, p₂, p₃, . . . stacked on the buffer base 52, as shown inFIGS. 31 to 34 as a first modification.

Arrangement of Stack Separating Mechanism

As shown in FIG. 31, the stack separating mechanism 250 has a pluralityof separation pawl mounting plates 252 which extend along the conveyingdirection d and are disposed in the vertical direction on the opposinginner surfaces of standing plates 46a and 46b above the buffer base 52.A pair of opposing separation pawl mounting plates 252 are arranged soas not to become hooked with the flanges 38 of each pallet p in thevertical direction. In the first modification, the buffer base 52 isfixed at the same vertical position as that of the pallet table 32 ofthe unmanned vehicle 20 which is different from the above embodiment.

All the separation pawl mounting plates 252 on the standing plates 46aand 46b are supported so they can move vertically along guide shafts254a and 254b which are fixed to the corresponding standing plates 46aand 46b to extend in the vertical direction. The upper ends of the guideshafts 254a and 254b are respectively fixed to the upper ends of thecorresponding standing plates 46a and 46b through fixing members 256aand 256b, and lower ends thereof are-fixed to the buffer base 52.

As shown in FIG. 32, an air cylinder C_(D1) is integrally mounted on thecentral portion of each separation pawl mounting plate 252. A piston 258of each air cylinder C_(D1) is arranged to extend downward. The lowerend of the piston 258 is fixed to the upper end of each air cylinderC_(D1) mounted on the corresponding separation pawl mounting plate 252located immediately therebelow. Each air cylinder C_(D1) comprises twoinput ends 260a and 260b. One input end 260a communicates with acylinder chamber above the piston 258, and the other input end 260bcommunicates with a cylinder chamber below the piston 258.

One input end 260a of each of all of the air cylinders C_(D1) isconnected to one output end 264a of a switching valve 264 through oneintroduction pipe 262a. The other input end 260b is connected to theother output end 264b of the switching valve 264. An input end 264c ofthe switching valve 264 is connected to a compressor (not shown) throughan introduction pipe 262c.

With the above arrangement, when the switching valve 264 is switched tooutput compressed air from one output end 264a, the compressed air isintroduced into the cylinder chamber above the piston 258 of each aircylinder C_(D1), and the corresponding piston is biased downward. Inother words, when the compressed air is supplied to one input end 260aof each air cylinder C_(D1), an interval between two adjacent separationpawl mounting plates 252 is increased, as shown in FIG. 32.

On the other hand, when the switching valve 264 is switched to outputcompressed air from the other output end 264b, the compressed air isintroduced into the cylinder chamber below the piston 258 of each aircylinder C_(D1) through the other introduction pipe 262b, and eachpiston 258 is biased upward. In other words, when the compressed air issupplied to the other input end of each air cylinder C_(D1), an intervalbetween two adjacent separation pawl mounting plates 252 is decreased asshown in FIG. 33.

In the narrowed state shown in FIG. 33, if pallets p are 25-mm thickpallets p₁, the disposition pitch of the separation pawl mounting plates252 is set to be 25-7=18 mm. In the widened state shown in FIG. 32,since pallets must be free from the 7-mm fitting margin, the dispositionpitch of the separation pawl mounting plates 252 is set to be, e.g., 30mm larger than the 25 mm mentioned above. In other words, when thecompressed air is supplied to one input end 260a of each cylinder C_(D1)from the state illustrated in FIG. 33, each piston 258 is pusheddownward by 12 mm, and the disposition pitch of the separation pawlmounting plates 252 is widened.

As shown in FIG. 34, the stack separating mechanism 250 comprisesseparation pawls 266 which are respectively mounted on the lowersurfaces of the separation pawl mounting plates 252 to be retractablealong a direction perpendicular to the conveying direction d. Morespecifically, a pair of opposing separation pawls 266 are retractablyarranged between a projecting position in which each pawl is hooked bythe corresponding flange 38 of each pallet p from the lower directionand a retracted position spaced apart from the corresponding flange 38.An air cylinder C_(D2) for retractably driving each separation pawl 266is attached to the lower surface of the separation pawl mounting plate252 outside the corresponding separation pawl 266. A piston 268 of eachair cylinder C_(D2) is reciprocally moved in a direction perpendicularto the conveying direction d. The distal end of each piston 268 isconnected to the corresponding separation pawl 266.

With the above arrangement, in a state wherein no compressed air issupplied to the air cylinders C_(D2), the pistons 268 are biased to theretracted positions, and all the separation pawls 266 are separated fromthe flanges 38 of the corresponding pallets p₁. When the compressed airis supplied to the air cylinders C_(D2), the separation pawls 266project from the retracted positions to the projecting position, and theseparation pawls 266 can be hooked with the flanges 38 of thecorresponding pallets p₁ from the lower direction.

Operation of the Stack Separating Mechanism

The simultaneous stack separating operation in the slack separatingmechanism 250 with the above arrangement will be described hereinafter.

When a stack of a plurality of pallets p₁ are conveyed onto the buffer52, compressed air is supplied to the air cylinders C_(D2), and theseparation pawls 266 are deviated from their retracted positions to theprojecting positions and can be hooked with the flanges 38 of thecorresponding pallets p₁ from the lower direction. Thereafter,compressed air is supplied to the first input ends of the air cylindersC_(D1), and the separation pawls 266 are deviated upward to widen thedisposition pitch thereof. In this manner, the separation pawls 266 arehooked with the flanges 38 from the lower direction, and each pallet p₁is set in a state wherein it can be drawn out sidewards from a pallet p₁immediately therebelow.

As has been described above, according to the first modification, aplurality of pallets p₁ stacked on the buffer base 52 are simultaneouslyseparated from each other by utilizing the stack separating mechanism250, and can be set in a state wherein they can be drawn out sideways.For this reason, as described above, even if a pallet p₁ retains thesame parts, the number of which is detected as 1 by the robot 12, islocated at any vertical position on the buffer base 52, the pallet p₁can be drawn out from that position to the elevator 26, and theoperation time can be satisfactorily shortened as compared with a caseusing the separation mechanism 64 of the above embodiment.

In the control operation of the FAC system with such a buffer, thedraw-out position of a pallet separated by the buffer to the elevator isfixed for each pallet. Therefore, the standby position in palletreplacement preparation of the elevator differs depending on the palletto be drawn out from the buffer. For this purpose, if the elevator hasdata shown in FIG. 25A as in the buffer, it can detect the position ofparts requested by the stocker in response to the replacementpreparation instruction from the robot.

Description of the Second Modification

In the elevator 26 of the embodiment described above, the common servomotor M_(E2) is used as a drive source for moving the three hooks 108,116, and 126 of the replacing mechanism 96 in the conveying direction d.However, the present invention is not limited to this. As shown in FIGS.35 to 39 as a second modification, a drive motor for driving the hooks108 and 116 for moving a pallet p filled with parts x in the conveyingdirection d, and a drive motor for driving the hooks 126 for moving anempty pallet p' in the conveying direction d may be separately arranged.

Description of the Elevator

As shown in FIG. 35, elevator 300 according to the second modificationhas the same elevator body 86 as that of the above embodiment, exceptthat guide grooves 102 and 132 are formed on its upper and lowersurfaces. The replacing mechanism 96 comprises a full pallet replacingmechanism 96a, mounted on the lower surface of a top plate 86a of theelevator body 86, for replacing a pallet p filled with parts x, and anempty pallet replacing mechanism 96b, mounted on the lower surface of abottom plate 86b of the elevator body 86, for replacing an empty palletp'.

As shown in FIGS. 36 and 37, the full pallet replacing mechanism 96acomprises a pair of first guide members 302a and 302b extending in theconveying direction d on the lower surface of the top plate 86a of theelevator body 86. The first slide plate 304 is supported by the firstguide members 302a and 302b to be reciprocal in the conveying directiond.

A projecting portion 308 threadably engaged with a first ball screw 306(to be described later) is integrally formed at the central portion ofthe first slide plate 304. The front and rear ends of the first ballscrew 306 are rotatably supported through a pair of first rotarysupporting members 310a and 310b fixed to the lower surface of the topplate 86a. The first ball screw 306 is rotated by a first servo motorM₁. Upon rotation of the rotating shaft of the first servo motor M₁, thefirst ball screw 306 is rotated, so that the first slide plate 304 isreciprocally moved along the conveying direction d.

The first slide plate 304 is formed to extend in a directionperpendicular to the conveying direction d. The first hooks 108 areretractably formed at two ends of the first slide plate 304 through aircylinders C_(E1) on the side of the buffer 22, and the second hooks 116are retractably formed thereon through air cylinders C_(E2) on the sideof the stocker 24, in the same manner as in the above embodiment. Thepairs of first and second hooks 108 and 116 are formed to have shapescapable of being engaged, from both sides, with the first notches 38a onthe side of the elevator 26 and the second notches 38b on the side ofthe unmanned vehicle 20 formed in the flanges 38 of each of pallets p₁,p₂, p₃, . . .

A pair of stationary slide guides 316 which are engaged with the firstor second hooks 108 or 116 and slidably support a pallet p which istaken in/pushed out in accordance with the pivotal motion of the firstservo motor M₁. The stationary slide guides 316 are arranged on thelower surface of the top plate 86a of the elevator body 86.Specifically, they are arranged to be slidable along the lower surfacesof the flanges 38 at both sides of a pallet p to be taken in/pushed out.

The vertical position of the upper edge of each stationary slide guide316 is set high enough to slidably support a pallet p₃ having a maximumthickness of 100 mm.

The empty pallet replacing mechanism 96b comprises a pair of secondguide members 322a and 322b extending in the conveying direction d onthe lower surface of the bottom plate 86b of the elevator body 86. Asecond slide plate 324 is supported by the second guide members 322a and322b to be reciprocal in the conveying direction d.

A projecting portion 328 threadably engaged with a second ball screw 326(to be described later) is integrally formed on the central portion ofthe second slide plate 324. The front and rear ends of the second ballscrew 326 are rotatably supported through a pair of second rotarysupporting members 330a and 330b fixed on the lower surface of thebottom plate 86b. The second ball screw 326 is driven by a second servomotor M₂. In this manner, upon rotation of the rotating shaft of thesecond servo motor M₂, the second ball screw 326 is rotated, so that thesecond slide plate 324 is reciprocally moved in the conveying directiond.

The second slide guide 324 is formed to extend in a directionperpendicular to the conveying direction d. Hook members 332 integrallyhaving third hooks 126 on the side of the stocker 24 are mounted on twoends of the lower surface of the second slide plate 324 to be slidablein a direction perpendicular to the conveying direction d. The thirdhooks 126 are formed into shapes capable of being engaged, from bothsides, with the 10 second notches 38b formed in the flanges of each ofthe pallets p₁, p₂, p₃, . . . on the side of the unmanned vehicle 20.

Second air cylinders C₂ are mounted on both ends of the slide plate 324to extend in a direction perpendicular to the conveying direction d. Thehook member 332 is connected to the distal end portion of a secondpiston 334 of each second air cylinder C₂. In this manner, upon drivingof the second air cylinders C₂, the third hooks 126 are reciprocallymoved to be engaged with/disengaged from the second notches 38b of theflanges 38.

A pair of movable slide guides 336 for slidably receiving an emptypallet p' taken out from the stocker 24 by the third hooks 126 aredisposed on the lower surface of the bottom plate 86b of the elevatorbody 86. The movable slide guides 336 are slidably arranged in adirection perpendicular to the conveying direction d, i.e., to beseparated from the received empty pallet p', in order to place thereceived empty pallet p' on the unloading rollers 78 of the unloadingmechanism 76. More specifically, as shown in FIGS. 38 and 39, themovable slide guides 336 are slidably mounted on the lower surface ofthe bottom plate 86b of the elevator body 86 through slide members 338,respectively. Third air cylinders C₃ for reciprocating the movable slideguides 336 are mounted on both sides of the lower surface of the bottomplate 86b. The movable slide guide 336 is connected to the distal endportion of a third piston 340 of each third air cylinder C₃. In thismanner, upon driving the third air cylinder C₃, the movable slide guides336 are reciprocally moved to be engaged with/disengaged from theflanges 38 of an empty pallet p'.

In the replacing mechanism 96 having the full and empty pallet replacingmechanisms 96a and 96b with the above arrangements, the replacingoperation of the pallets p and p' are the same as that of the replacingmechanism 96 in the above embodiment, except that the first and secondhooks 108 and 116 are simultaneously driven, and therefore, a detaileddescription thereof will be omitted.

As described above, in the second modification, when a drive source forreplacing a full pallet p and a drive source for replacing an emptypallet p' comprise the separate servo motors M₁ and M₂, the same effectas in the arrangement of the embodiment can be provided.

In the control operation associated with the second modification, thethree hooks of the elevator are driven by two motors rather than thesingle motor in the above embodiment. Thus, a detailed descriptionthereof will be omitted.

Description of Third Modification

In the elevator 26 of the embodiment described above, three hooks 108,116, and 126 are provided for the replacing mechanism 96. The first andsecond hooks 108 and 116 are arranged at an upper stage to take in andpush out a full pallet p, and the third hooks 126 are placed at a lowerstage to draw in an empty pallet p'. However, the present invention isnot limited to this. As shown in FIGS. 40 and 41 as a thirdmodification, a replacing mechanism 350 can be comprised of only thefirst and second hooks 108 and 116 and not the third hooks.

Description of Replacing Mechanism

More specifically, as shown in FIG. 40, in elevator 26 a cut-off portion86c is formed in the central portion of a bottom plate 86b of theelevator body 86 along the conveying direction d. A pallet p can pass inthe conveying direction through the cut-off portion 86c.

The air cylinder supporting plates 112 extending in the conveyingdirection d are respectively fixed to both ends of the slide plate 106.A first air cylinder C_(E1) for reciprocally moving the correspondingfirst hook 108 is attached to the end portion of each air cylindersupporting plate 112 on the side of the buffer 22. The first hook 108 isconnected to the distal end portion of a first piston 114 of each firstair cylinder C_(E1). In this manner, upon driving the first aircylinders C_(E1), the first hooks 108 are reciprocally moved to beengaged with/disengaged from the first notches 38a of the flanges 38.

The second hooks 116 are mounted on two end portions of the sidesurfaces, on the side of the stocker 24, of the slide plate 106 throughsecond hook slide members 118 to be slidable along the longitudinaldirection of the slide plate 106, i.e., in a direction perpendicular tothe conveying direction d. The pair of second hooks 116 are formed tohave shapes capable of being engaged, from two sides, with the secondnotches 38b formed in the flanges 38 of each of pallets p₁, p₂, p₃ . . .on the side of the unmanned vehicle 20.

Second air cylinders C_(E2) for reciprocally driving the second hooks116 are mounted on the end portions, on the side of the stocker 24, ofthe air cylinder supporting plates 112 fixed to the two ends of theslide plate 106. The second hooks 116 are connected to the distal endportions of second pistons 120 of the second air cylinders C_(E2). Inthis manner, upon driving of the second air cylinders C_(E2), the secondhooks 116 are reciprocally moved to be engaged with/disengaged from thesecond notches 38b of the flanges 38.

A pair of movable slide guides 352 for slidably receiving a full palletp taken in from the buffer 22 by the first hooks 108 and an empty palletp' drawn in from the stocker 24 by the second hooks 116 are disposed onthe bottom plate 86b of the elevator body 86.

The movable slide guides 352 are arranged to be slidable in a directionperpendicular to the conveying direction d, i.e., to be separated froman empty pallet p' received therein in order to place the empty palletp' received therein on the unloading rollers 78 of the unloadingmechanism 76. That is, slide members 354 are mounted on the bottom plate86b of the elevator body 86 so as to slidably support the movable slideguides 352 in a direction perpendicular to the conveying direction d.

Fourth air cylinders C_(E4) for reciprocally driving the movable slideguides 352 are mounted adjacent to the central portions of the two sideedges along the conveying direction d of the cut-off portion 86c on thebottom plate 86b. The movable slide guides 352 are connected to thedistal end portions of the fourth pistons 256 of the fourth aircylinders C_(E4). In this manner, upon driving the fourth air cylindersC_(E4), the movable slide guides 352 are reciprocally moved to beengaged with/disengaged from the flanges 38 of an empty pallet p'.

The replacing mechanism 350 according to the third modification isarranged as described above. Thus, after an empty pallet p' istemporarily taken in from the stocker 24 onto the movable slide guides352, the empty pallet p' is temporarily placed on the unloadingmechanism 76, and the unloading mechanism 76 is moved downward to removethe empty pallet from the replacing mechanism 350. In the state whereinthe empty pallet p' is separated from the replacing mechanism 350 andthe interior of the elevator body 86 becomes empty again, the replacingmechanism 350 is moved upward to a vertical position adjacent to theseparation position so as to receive a full pallet p separated by thebuffer 22. At this separation position, the replacing mechanism 350receives the full pallet p from the buffer 22, and pushes out the fullpallet p to the predetermined position of the stocker 24 which is emptysince it took in an empty pallet p'.

In this manner, a series of pallet replacing operations are completed.

Control

The operation of the elevator according to the third modification willbe described hereinafter with reference to FIGS. 42A to 42H togetherwith the movement of the stocker. In the control operation of thismodification, control of the robot is given in step S26, and the basiccontrol operation of the embodiment need not be modified. Therefore,robot control uses FIGS. 23A and 23B, stocker control uses FIGS. 24A and24B, and buffer control uses FIGS. 25B and 25C. For the elevator, thecontrol operation sequence will be explained with reference to FIGS. 42Ato 42H. Since the empty pallet draw-out mechanism of the basicembodiment is removed from the lower portion, the elevator of thismodification uses the sequence of drawing-out the empty pallet from thestocker stacking the empty pallet the insertion of a new pallet.

In FIG. 42A, if a remaining parts count Z L₀ ! of a pallet of a processnumber L₀ (placed on a shelf S L₀ !) becomes 1, the robot issues apallet replacement preparation Instruction to the buffer and theelevator. Upon reception of the preparation instruction, the bufferchecks the position of a pallet to be placed on the buffer base 52 basedupon the parts name and the like, corresponding to the process L₀ (=D₀)in accordance with the buffer control of the above-mentioned basicembodiment (FIG. 25A). The pallet is separated at the separationposition. On the other hand, upon reception of the replacementpreparation instruction, the modified elevator is moved to itsreplacement standby position. The standby position corresponds to thestocker position S L₀ ! in the process L₀. When the elevator arrives atthe standby position, the present process used by the stocker will shiftto another process L'. After a cycle of the processes, the remainingparts count Z L₀ ! of the pallet on the shelf S L₀ ! becomes zero whenit arrives at the draw-out base 154 position of the robot. In this case,the draw-out operation of the empty pallet from the stocker to theelevator is performed (FIGS. 42C and 42D). After the empty pallet istaken in, the elevator is moved downward to stack the empty pallet onthe unloading mechanism 76 (FIG. 42E). In this case, the elevator holdsno pallet.

Thereafter, the elevator is moved upward to the separation position ofthe buffer, and takes a separated new pallet therein. After the take-inoperation, the elevator issues a take-in completion message to thebuffer, and is then moved downward to the standby position S L₀ ! of thestocker in a stationary state (FIG. 42F). The elevator moves downward tothe standby position of the stocker pushes a new pallet into the stocker(FIGS. 42G and 42H), and sends a replacement completion message to thestocker. Upon reception of this message, the stocker restarts feedingparts to the robot.

As described above, although according to the third modification, thereplacement operation of the empty pallet p and the full pallet p takesslightly longer time than that in the above embodiment, the arrangementof the replacing mechanism 350 can be simplified, thus reducing cost.

Description of Fourth Modification

Arrangement

In the unloading mechanism 76 of the above-mentioned embodiment, emptypallets p' separated from the elevator 26 at a lower position are heldin a stacked state. When the number of stacked empty pallets p' hasreached a predetermined value, the unloading mechanism 76 is driven tounload the pallets to a position below the buffer base 52, i.e., aposition adjacent to the empty pallet table of the unmanned vehicle 20.In particular, in the above description, the unloading mechanism 76 isfixed in the lower position (and cannot move vertically). However, thepresent invention is not limited to this. As shown in FIGS. 43 and 44 asa fourth modification, a portion of the unloading mechanism 76 locatedbelow the elevator 26 may move vertically, and may comprise a so-calledlift mechanism.

More specifically, as shown in FIG. 43, the unloading mechanism 76according to the fourth modification comprises a stationary conveymechanism 400 located below the buffer base 52, and a lift mechanism 402located below the elevator 26. The stationary convey mechanism 400 hasthe same arrangement as that of the unloading mechanism 76 described inthe above embodiment, and a detailed description thereof will beomitted.

In the lift mechanism 402 as shown in FIG. 43, other slidable members404 are attached to guide members 88 mounted on columns 82a, 82b, 82c,and 82d constituting the elevator 26 so as to be located below slidablemembers 90 to which the elevator body 86 is attached. A lift base 406 isvertically movable and is supported at four corners by these fourslidable members 404. Unloading rollers 78b are arranged on the liftbase 406. When the lift base 406 is brought to its lowest position, theunloading rollers 78b horizontally match unloading rollers 78aconstituting the stationary convey mechanism 400.

A projection 408 is integrally mounted on the side surface of the liftbase 406 to extend in a gap between the far-side columns 82b and 82d inFIG. 43. An air cylinder mounting member 410 is provided so as to bebridged between the columns 82b and 82d and to extend horizontally. Anair cylinder C_(L) is mounted on the upper surface of the air cylindermounting member 410 and extends downward. The lower end of a piston 412of the air cylinder C_(L) is fixed to the uppper surface of theprojection 408.

Note that the air cylinder C_(L) comprises a brake mechanism (not shown)capable of arbitrarily setting a projectable amount of the piston 412.In the normal state, the air cylinder C_(L) is held in a state whereinthe piston 412 projects to a maximum amount. When compressed air issupplied to the cylinder, the cylinder pulls up the piston 412, in otherwords, reduces the projecting amount in order to move the lift base 406upward.

A sensor mounting member 414 is attached to the lower surface of thecylinder mounting member 410 and extends downward. Three sensors S₁, S₂,and S₃ are arrayed in the vertical direction on the sensor mountingmember 414 and can oppose the lift base 406 which is vertically moved.

These sensors S₁, S₂, and S₃ are disposed so as to select one of threelift positions (uppermost standby positions) the uppermost one of theempty pallets p' is placed on the lift base 406 for the followingreason, i.e., to select one of three positions at which the lift base406 is moved upward and waits when an empty pallet p' is released fromthe elevator body 86 onto the lift base 406.

More specifically, as shown in FIG. 44, the height from the base to thebottom surface of an empty pallet p₁ ', p₂ ', or p₃ ' changes dependingon the height of the empty pallet p₁ ', p₂ ', or p₃ ' held below theelevator body 86 at the lowermost position. For this reason, downwardmovement control of the elevator body 86 when the empty pallet p₁ ', p₂', or p₃ ' held below the elevator body 86 is released onto the emptypallets p' on the lift base 406 becomes complicated, and it is difficultto determine the upward movement position of the lift base 406.

In other words, if the lift base 406 is moved upward to a predeterminedstandby position while the draw-in operation of the empty pallets p₁ ',p₂ ', and p₃ ' is performed in the elevator 26, the downward movementtime of the elevator body can be minimized, and the subsequentoperations can be quickly performed. In this manner, these sensors S₁,S₂, and S₃ aim at simplifying downward movement control of the elevatorbody 86 and shortening the downward movement time, and cause the liftbase 406 to wait at an upward standby position in accordance with theheight of empty pallet p₁ ', p₂ ', or p₃ ' to be stacked on the liftbase 406.

Thus, the sensor S₁ at the uppermost position is positioned below thevertical position of the lower surface of the empty pallet p₁ ' by apredetermined distance L when the elevator body 86 is located at thelowermost position and the height of the empty pallet p' held below theelevator body 86 is 25 mm.

The sensor S₂ at the second highest position is positioned 25 mm belowthe sensor S₁. More specifically, the second sensor S₂ is positionedbelow the vertical position of the lower surface of the empty pallet p₂' by the predetermined distance L when the elevator body 86 is locatedat the lowermost position and the height of the empty pallet p' heldbelow the elevator body 86 is 50 mm.

The sensor S3 at the third highest position is positioned 50 mm belowthe sensor S₂. More specifically, the second sensor S₂ is positionedbelow the vertical position of the lower surface of the empty pallet p₃' by the predetermined distance L when the elevator body 86 is locatedat the lowermost position and the height of the empty pallet p' heldbelow the elevator body 86 is 100 mm.

The predetermined distance L is set small enough to allow, when theempty pallet p₁ ', p₂ ', or p₃ ' is released from the elevator body 86onto the lift base 406 while keeping this distance, the released emptypallet p₁ ', p₂ ', or p₃ ' to be stacked on the empty pallets p' on thelilt base 406.

In this manner, when the elevator body 86 transfers the empty pallet p₁', p₂ ', or p₃ ' held thereon to the empty pallets stacked p' on thelift base 406, the uppermost position of the empty pallets p' stacked onthe lift base 406 is brought in advance to an upward standby positioncorresponding to the lowermost position of the elevator body 86 and theheight of the empty pallet p₁ ', p₂ ', or p₃ ' held thereon. As aresult, the elevator base 86 need only be moved downward to itslowermost position, thus simplifying the downward movement control andshortening the downward movement time.

Control

Operation control in the fourth modification with the above arrangementwill be briefly described hereinafter with reference to FIG. 45. Controlof this modification can be achieved by modifying steps S226 to S236 inFIG. 26A. More specifically, when the replacement request of the emptypallet p' is issued in step S76 or S108 in the stocker controloperation, the elevator body performs the above-mentioned predeterminedoperation, and replaces the empty pallet p' with a new pallet p in stepS220 (FIG. 26A).

The lift mechanism waits for the replacement request in step S420 (FIG.45). Upon reception of this request, the lift mechanism detects thethickness of the empty pallet held on the elevator in step S422. Whenthe thickness is detected, the air cylinder C_(L) is driven in step S424to move the lift base 406 upward to one of the positions of the sensorsS₁ to S₃ corresponding to the detected thickness. In step S426, the liftmechanism issues the standby position arrival message to the elevator,and waits for a release message of the empty pallet p' from theelevator.

The elevator which completed pallet replacement sends a messageindicating this to the stocker in step S222 (FIG. 26A), and causes theelevator body to move downward to the position illustrated in FIG. 43 instep S400 (FIG. 45). At this position, the elevator waits for thestandby position arrival message from the lift mechanism. When themessage has been received from the lift mechanism, the distance betweenthe empty pallet p' held below the elevator and the uppermost emptypallet p' on the lift base 406 almost becomes the distance L, as hasbeen described above. In step S404, the empty pallet held below theelevator is released, and in step S406, a release message is sent to thelift mechanism.

Upon reception of the release message, the flow advances from step S428to step S430, and the lift mechanism causes the lift base 406 to movedownward to the floor position. At this time, it is checked if the thevertical position of the presently stacked empty pallet p' has reachedthe maximum height sensor position. If the maximum height position hasbeen reached, this interfers with the vertical movement of the elevator.Therefore, in step S434, the stationary convey mechanism 400 is drivento unload the stacked empty pallets.

Under such control of the elevator and lift mechanism, the elevator body86 need only be moved downward to its lowermost position. Thus, thedownward movement control can be simplified, and the downward movementtime can be shortened.

In the elevator control of the above-mentioned basic embodiment, thethickness of the empty pallet is given as H L!. If this thickness iserroneously detected, the elevator body may be damaged. For this reason,the following auxiliary mechanism may be arranged as a means forchecking the thickness of the empty pallet. More specifically, althoughnot shown, in order to detect the height of the empty pallet p₁ ', p₂ ',or p₃ ' drawn below the elevator body 86, sensors for detecting theheight of these empty pallets held below the elevator body 86 areprovided on the lower portion of the elevator body 86 to collate thedata H L! with the thickness detected by the sensors (not shown).

The number of the above three sensors S₁ to S₃ can be reduced to one. Inthis case, one sensor can be commonly used as the maximum height sensorS₄. In this case, however, the empty pallet held below the elevator bodyand the stacked empty pallets take three different distances inaccordance with the thicknesses of the pallets. Therefore, the elevatorbody must be further moved downward to shorten the distance so as toallow the elevator body to release the empty pallet.

ANOTHER EMBODIMENT Arrangement

In the description of the previous embodiment, the parts feeding system14 for feeding necessary parts x to the robot 12 comprises the buffer 22for separately receiving parts from the unmanned vehicle 20 andtemporarily retaining the received parts, the stocker 24, arrangedadjacent to the robot 12, for sequentially feeding parts necessary forassembly to the robot 12 in accordance with the assembling order, andthe elevator 26, disposed between the buffer 22 and the stocker 24, fortransferring parts short in the stocker 24 from the buffer 22 to thestocker 24.

In particular, in the previous embodiment, a replacing position (atwhich an empty pallet whose remaining parts count becomes zero isreplaced with a full pallet p filled with corresponding parts) is aposition (in a process L+1) of an empty pallet which was located at adraw-out position of the robot 12 in the process L. In other words, thereplacing position is defined by the process order L and the shelfposition S L! corresponding to the process. The replacing position mayoften be different from the separation position at the buffer 22.Therefore, the elevator 26 for transferring full pallets p from thebuffer 22 to the stocker 24 is necessary between these positions.

However, the present invention is not limited to the arrangement of theprevious embodiment, and may employ an arrangement of anotherembodiment, as shown in FIGS. 46 to 49.

In this embodiment, the separation position in the buffer 22 and thereplacing position in the stocker 24 are set at an identical verticalposition, and the separation position in the buffer 22 is setimmediately above the buffer base 52. With this arrangement, theelevator 26 necessary in the previous embodiment can be omitted.

An arrangement of an FAC 10 according to this embodiment will bedescribed hereinafter in detail. The same reference numerals in thisembodiment denote the same parts as in the arrangement of the previousembodiment and its various modifications, and a detailed descriptionthereof will be omitted.

As shown in FIG. 46, a parts feeding system 14 for feeding necessaryparts to a robot 12 comprises a buffer 450 for receiving parts from anunmanned vehicle 20 and temporarily retaining the received parts, and astocker 24, disposed between the buffer 450 and the robot 12, forsequentially feeding parts necessary for assembly to the robot 12 inaccordance with the assembling order.

Unlike the buffer 22 in the previous embodiment, the buffer 450 has afunction of temporarily receiving an empty pallet p' from the stocker 24and pushing out a pallet separated therefrom to the replacing positionof the stocker 24. In addition, pallets p are stacked in an order,starting from the lowermost pallet, such that the remaining parts countbecomes zero in the stocker 24. A buffer base 52 is mounted while itsvertical position is fixed.

More specifically, the buffer 450 comprises the buffer base 52 fixed atthe same vertical position as that of a pallet table 32 of the unmannedvehicle 20. Moreover, buffer 450 is sandwiched between standing plates46a and 46b through spacer blocks 452, as shown in FIG. 47. In otherwords, the side surfaces of the buffer base 52 are separated from thecorresponding standing plates 46a and 46b by the lengths of the spacerblocks 452.

A separation mechanism 454 for independently separating a pallet pdirectly placed on the buffer base 52 from the pallets locatedthereabove is provided above the buffer base 52.

The separation mechanism 454 comprises mounting members 456 respectivelyfixed on the upper ends of the standing plates 46a and 46b. Parallelguide shafts 458 extending downward are mounted on the two end portionsof each mounting member 456 along the conveying direction d. Aseparation pawl mounting plate 460 is attached to the lower ends of eachpair of guide shafts 458 along the conveying direction d. A pair ofseparation pawls 462 which can hook flanges 38 of a pallet p from thelower direction are mounted on the lower surface of each separation pawlmounting plate 460 to be retractable in a direction perpendicular to theconveying direction d.

A ball screw 464 extending in the vertical direction is rotatablysupported at the central portion of each mounting member 456. The lowerend of each ball screw 464 is rotatably supported by a supporting plate466 fixed to the corresponding one of the standing plates 46a and 46b. Aball screw receiving portion 468 with which the central portion of eachball screw 464 engages is formed at the central portion of eachseparation pawl mounting plate 460.

A servo motor M_(T) is mounted on the upper surface of the far-sidemounting member 456 in FIG. 47 through a stay 470. The upper end of theball screw 464 is connected to the driving shaft of the servo motorM_(T). Upon rotation of the driving shaft, the ball screw 464 isrotated.

A driving pulley 472 is coaxially mounted on the driving shaft of themotor M_(T). A driven pulley 472 is coaxially mounted on the upper endof the near-side ball screw 464 in FIG. 47. A timing belt 476 is loopedbetween the driving pulley 472 and the driven pulley 474. In thismanner, the pair of ball screws 464 are synchronously rotated. Morespecifically, both the separation pawl mounting plates 460, i.e., theseparation pawls 462 are vertically moved while maintaining the samevertical positions.

In order to retractably drive the separation pawls 462 from thecorresponding separation pawl mounting plates 460, air cylinders C_(T1)are provided on the rear surface of each separation pawl mounting plate460. The distal end of a piston (not shown) of each air cylinder C_(T1)is connected to the corresponding separation pawl 462. Each separationpawl 462 is retractably supported through a pair of guide pins 478.

In a state wherein no compressed air is supplied, each air cylinderC_(T1) biases the corresponding separation pawl 462 to the retractedposition separated from the flange 38. In a state wherein the compressedair is supplied, each cylinder C_(T1) biases the correspondingseparation pawl 462 to the projecting position at which the pawl 462 canhook the flange 38.

With the above arrangement of the separation mechanism 454, when alowermost pallet pa, i.e., a pallet pa which is directly stacked on thebuffer base 52 and is next to be transferred to the stocker 24, isseparated from the plurality of pallets p stacked on the buffer base 52,the separation pawls 462 are moved through the servo motor M_(T) topositions immediately adjacent and below the flanges 38 of a secondlowermost pallet pb while being biased to their retracted positions.

Thereafter, compressed air is supplied to the air cylinders C_(T1) tobias the separation pawls 462 to their projecting positions. In thisstate, the separation pawls 462 can engage with the flanges 38 of thesecond lowermost pallet pb on the buffer base 52 from below. From thisstate, the servo motor M_(T) is starts moving the separation pawlmounting plates 460, i.e., separation pawls 462 upward.

In this manner, the second lowermost pallet pb is moved upward togetherwith the pallets p stacked thereon. In other words, the second lowermostpallet pb and the pallets p stacked thereon are lifted up while thelowermost pallet pa is left on the buffer base 52. Lowermost pallet pband the pallets p stacked thereon are thus separated from the lowermostpallet pa. Therefore, the separated lowermost pallet pa, i.e., thepallet pa to next be transferred to the stocker 24, can be set in astate wherein it can be independently drawn out along the conveyingdirection d.

The buffer 450 comprises a replacing mechanism 480 of pallets p whichare located around the buffer base 52. The replacing mechanism 480comprises a horizontal slide plate 484 which is arranged below thebuffer base 52 to be reciprocally movable in the conveying direction dthrough a pair of guide shafts 482a and 482b, as shown in FIGS. 48 and49. A ball screw 486 is disposed along the conveying direction d at thecentral portion of the lower surface of the buffer base 52 such that twoends thereof are rotatably through supporting members 488a and 488b, asshown in FIG. 48. The slide plate 484 is arranged to be in rollingcontact with the lower surface of the buffer base 52 through a pair ofrollers 484a and 484b.

The ball screw 486 is threadably engaged with a threadably engagedportion 484c integrally formed at the central portion of the slide plate484. Although not shown, the ball screw 486 is rotated by a servo motor.As a result, the slide plate 484 is reciprocally moved in the conveyingdirection d by threadable engagement between the ball screw 486 and thethreadably engaged portion 484c.

A pair of first hooks 490a and 490b for drawing in an empty pallet p'from the stocker 24 and holding the drawn pallet below the buffer base52 are mounted on the lower surface of the slide plate 484 to beretractably movable in a direction perpendicular to the conveyingdirection d. Air cylinders C_(T2) for reciprocally driving the firsthooks 490a and 490b, respectively, are attached to the lower surface ofthe slide plate 484. Pistons 492 of air cylinders C_(T2) are connectedto the first hooks 490a and 490b.

When compressed air is not supplied to the air cylinders C_(T2), the aircylinders C_(T2) are operated to bias the corresponding first hooks 490aand 490b to positions separated sidewards from the flanges 38 of thepallet p. When compressed air is supplied to the air cylinders C_(T2),the cylinders C_(T2) are operated to move the corresponding first hooks490a and 490b so as to engage with second notches 380 of the flanges 38of the pallet p.

The replacing mechanism 480 comprises movable slide guides 494a and 494bfor receiving an empty pallet p' drawn from the stocker 24 by the firsthooks 490a and 490b. The movable slide guides 494a and 494b are providedto the corresponding standing plates 46a and 46b through guide pins 496aand 496b to be retractable in a direction perpendicular to the conveyingdirection d. The movable slide guides 494a and 494b are mounted on thedistal ends of pistons 498 of air cylinders C_(T3) fixed to thecorresponding standing plates 46a and 46b, respectively.

When compressed air is not supplied to the air cylinders C_(T3), the aircylinders C_(T3) bias the corresponding movable slide guides 494a and494b to their projecting positions at which the guides hook the flanges38 of a drawn empty pallet p'. When compressed air is supplied to theair cylinders C_(T3), the air cylinders C_(T3) bias the correspondingmovable slide guides 494a and 494b to their retracted positionsseparated sidewards from the flanges 38 of the drawn empty pallet p'.

The replacing mechanism 480 comprises a pair of second hooks 500a and500b for pushing a full pallet p into the stocker 24 while being locatedat side portions above the buffer base 52. The second hooks 500a and500b can be engaged with the second notches 38b of the flanges 38 of thefull pallet p from two sides thereof. The second hooks 500a and 500b aremounted on the distal ends of pistons 504 of air cylinders C_(T4) fixedon the upper surfaces of supporting stays 502a and 502b which areintegrally connected to the slide plate 484.

When compressed air is not supplied to the air cylinders C_(T4), the aircylinders C_(T4) bias the corresponding second hooks 500a and 500b totheir retracted positions separated sidewards from the flanges 38. Whencompressed air is supplied to the air cylinders C_(T4), the aircylinders C_(T4) bias the corresponding second hooks 500a and 500b totheir projecting positions at which the hooks engage with the secondnotches 38b of the flanges 38.

As described above, in this embodiment comprising the above-mentionedbuffer 450, the stocker 24 has the same arrangement as that of theprevious embodiment, but its operation is slightly different from theprevious embodiment. More specifically, the stocker 24 in the previousembodiment is operated such that the draw-out position of each pallet pin the elevating frame 152 is vertically moved within a range whereinthe draw-out position can oppose the draw-out base 168. The stocker 24in this embodiment is operated such that the draw-out position pallet pin the elevating frame 152 can oppose the separation position of thebuffer 450 while executing the above-mentioned operation.

In this embodiment, in order to place an empty pallet p' received by thelower portion of the buffer base 52 onto an unloading mechanism 76, theunloading mechanism 76 comprises a lift mechanism 402 having the samearrangement as that described in the fourth modification of the previousembodiment in a portion 10 below the buffer base 52.

Control

The control operation of the stocker 24 and the buffer 450 according tothis embodiment with the above arrangement will be described below withreference to FIGS. 50A and 50B. Note that general control for the robotuses the program shown in FIGS. 24A and 24B. The main features of thecontrol operation are as follows. Since there is no elevator like in theprevious embodiment, even if a pallet replacement preparation request isissued from the robot, only the buffer performs the preparationoperation. When the stocker 24 detects from the robot that the remainingparts count in the pallet becomes zero (the replacement request flag IL!=1), it temporarily interrupts parts feeding to the robot (i.e., doesnot enter the next process), and moves the elevating frame 152 to thepallet separation position by the buffer described above. Replacement ofempty and full pallets is performed at this separation position.Thereafter, the stocker is moved according to the original process ordersuch that a pallet placed on a shelf position of the correspondingprocess matches with the draw-out position of the draw-out unit 154, andparts feeding to the robot is resumed.

FIG. 50A is a flow chart of the control program for the stockeraccording to this embodiment. Step S600 step S608 show control until theelevating frame 152 of the stocker 24 is vertically moved such that apallet, at a shelf position corresponding to a process number G (=L)received from the robot, is moved to the draw-out position of thedraw-out unit 154 and is drawn out at the position of the draw-out unit154. The pallet draw-out preparation completion message is sent to therobot in step S610. In step 611, a parts pick completion message fromthe robot is waited for. If the pick completion message is received, theflow advances from step S611 to step S612, and the pallet on thedraw-out unit 154 is returned into the elevating frame 152. In stepS614, it is checked if the replacement request flag I L! is set to be"1" by the robot.

If the flag is not set, steps S628 to S634 are executed, and the flowthen returns to step S606. The above-mentioned control is repeated untilthe replacement request flag I L! is set to be "1".

During the repetition of these steps, if the robot detects a palletwhose remaining parts count has become 1 (step S22 in FIG. 23A), areplacement preparation operation instruction must be issued to thebuffer in step S26 (FIG. 23A).

When the replacement preparation instruction is issued, the flowadvances from step S650 in the buffer control program shown in FIG. 50Bto step S652, and the thickness H D! of a new pallet is obtained basedon the process number D (D=G in step S24 in FIG. 23A) by searching acorresponding variable in the variable table (FIG. 21A). In step S654,the pallet at the lowermost position is separated. More specifically,the motor M_(T) is rotated until H D! moves the separation pawls 462upward. At this time, the air cylinders C_(T1) are driven to hook apallet on a stage immediately above or higher than that of the fullpallet to be separated by the separation pawls 462. After hooking, themotor M_(T1) is further rotated to move the pallet on a stageimmediately above or higher than that of the full pallet to beseparated, thereby separating the pallet to be separated. In thismanner, after the full pallet is separated from other pallets, aseparation completion message is sent to the stocker in step S655, andthe replacement request instruction is waited for in step S656.

If the stocker detects in step S614 that the robot has set the flag I L!to "1", the flow advances to step S616 and an empty pallet in theprocess L placed on a shelf S L! is moved upward to the empty palletdraw-out position shown in FIG. 50C. More specifically, after the upwardmovement, the position from the floor of the shelf on which the emptypallet is placed is a position matching the slide guides 494a (or 494b).In step S618, the empty pallet replacement request message is sent tothe buffer. In step S620, control waits until the draw-out mechanismbelow the buffer draws out the empty pallet.

Upon reception of the replacement request, the buffer performs thedraw-in operation of the empty pallet in step S658. That is, the aircylinders C_(T3) are driven to bias the slide guides 494a. Then, themotor (not shown) is rotated so that the first hooks 490a and 490b areslid in the stocker without being biased. The air cylinders C_(T2) aredriven to bias the hooks 490a and 490b to hook the empty pallet withthese hooks. Then, the motor (not shown) is rotated in the reversedirection to draw the empty pallet into the lower portion of the buffer.The flow advances to step S660, and an empty pallet draw-out completionmessage is sent to the stocker. Then, the stocker is moved to a push-inposition of a full pallet.

At this time, the buffer control operation is divided into two parallelcontrol operations. That is, the buffer waits for the push-out positionmovement completion message from the stocker in step S662a, and furtherwaits until the lift mechanism is moved upward to a position high enoughto allow an empty pallet release operation from the buffer in stepS662b.

The control operation of the lift mechanism 402 will be described below.The lift mechanism 402 has an arrangement equivalent to that of thefourth modification described above. Since the empty pallet draw-outmechanism of the buffer of this embodiment is of a fixed type, a liftposition must be accurately detected, as shown in FIGS. 43 and 44.Therefore, the control operation of the lift mechanism shown in FIG. 50Bis almost the same as that shown in FIG. 45. More specifically, when thelift mechanism 402 receives the replacement request message from thestocker in step S700, the flow advances to step S702 to check thethickness of an empty pallet in the stocker. In step S704, the lift base406 is moved upward to the sensor position (S₁, S₂, S₃ in FIG. 43)corresponding to the detected thickness. When the lift base 406 hasreached the standby position, a message indicating this is sent to thebuffer in step S706, and an empty pallet release message from the bufferis waited for in step S708.

Assuming that the lift mechanism arrives at the standby positionearlier, the flow advances from step S662b to step S662c, and the bufferreleases the empty pallet. More specifically, the air cylinders C_(T3)are returned to the release hooking position of the empty pallet. Instep S662d, a message indicating this is sent to the lift mechanism 402.Upon reception of this message, the flow advances to step S710, and thelift mechanism 402 causes the lift base 406 to move downward to thefloor position. It is then checked in steps S712 and S714 if the emptypallets are stacked on the lift base up to the maximum verticalposition.

When the stocker receives an empty pallet draw-out message from thebuffer in step S620, it causes an empty shelf to move upward to thepush-in position of a full pallet, as shown in FIG. 50D. When thecorresponding shelf reaches this position, the stocker sends a movementcompletion message to the buffer in step S624, and waits for acompletion message indicating a push-in operation of a new pallet intothe stocker from the buffer.

When the buffer receives the movement completion message in step S662a,it starts a push-out operation of the full pallet into the stocker instep S664. More specifically, the air cylinders C_(T4) bias the hooks500a and 500b to engage with the flanges of the pallet. Then, the motor(not shown) is rotated to push the full pallet into the shelf (FIG.50D). The air cylinders C_(T4) are returned, the motor is rotated in thereverse direction, and the push-in mechanism is returned into thebuffer. In step S666, a replacement completion message is sent to thestocker. In step S668, the motor M_(T) is rotated in the reversedirection to return onto rollers 54 the pallet which was lifted up bythe guides 460 and 462. The air cylinders C_(T) are returned to bedisengaged from the separation pawls 462.

In this manner, the draw-out control operation of an empty pallet at afixed position and a push-in control operation of a full pallet at afixed separation position are completed.

In the control program shown in FIG. 50B, the lift mechanism 402 beginsto move upward in response to the replacement request (remaining partscount=0), but may perform upward movement when the remaining parts countin a pallet becomes 1.

Modification of Another Embodiment

In the arrangement of the above embodiment, pallets p are stacked on thebuffer base 52 in the replacement request generation order in thestocker 24, starting from the lowermost pallet. A pallet which isseparated on the buffer base 52 to be transferred to the stocker 24 inthis manner is always a pallet p directly placed on the buffer base 52,i.e., a pallet p at the lowermost position. For this reason, theelevator 26 described in the previous embodiment is not necessary, andthe separation mechanism 454 and the replacing mechanism 480 need onlybe arranged near the buffer base 52.

However, the present invention is not limited to the arrangement of theabove embodiment. As shown in FIG. 51, as a modification of thisembodiment a variety of pallets p may be stacked on the buffer base 52in an arbitrary order.

As shown in FIG. 51, the modification of this embodiment comprises abuffer 22 having the same arrangement as that described in the previousembodiment. Therefore, in this modification, a predetermined pallet p isseparated by second separation pawls 68 of the buffer 22 from aplurality of pallets p arbitrarily stacked on a buffer base 52.

This modification comprises a transfer 550, as another mode of atransfer means, for transferring a pallet p separated at the buffer 22to the stocker which was moved upward to the same level as theseparation position while being adjacent to the separation position ofthe buffer 22.

The transfer 550 comprises an elevator body 86 which is arrangedadjacent to the separation position of the buffer 22 and is fixed inposition in the elevator mechanism in the arrangement of the previousembodiment. More specifically, the transfer 550 comprises the elevatorbody 86 fixed to four columns 82a to 82d as a transfer body 552. Thetransfer body 552 comprises a replacing mechanism 96 having the samearrangement as that in the previous embodiment.

In other words, in this modification, unlike in the above embodimentwherein the buffer 450 comprises the replacing mechanism 480, thetransfer 550 comprises the replacing mechanism 96 independent of thebuffer 22.

When this modification is arranged as described above, even if pallets pare stacked on the buffer base 52 in an arbitrary order, a pallet prequested by the buffer 22 is separated, and then, a pallet p filledwith parts can be supplied to a predetermined replacing position of thestocker 24 moved upward to the same level as the separation positionthrough the transfer 550.

An unloading mechanism 76 is used to place empty pallet p' drawn fromthe stocker 24 into the lower portion of the transfer 550. Thisunloading mechanism 76 comprises the lift mechanism 402 described in thefourth modification of the previous embodiment.

In the above description, the replacing mechanism 96 employs the samearrangement as that in the previous embodiment. However, the presentinvention is not limited to this. For example, an arrangement separatelycomprising a full pallet replacing mechanism 96a and an empty palletreplacing mechanism 96b as described in the second modification of theprevious embodiment may be employed.

Control according to this modification is basically similar to thatshown in FIG. 50A since the empty pallet replacing position is fixed.Movement to that position is performed by the stocker because noelevator is arranged. Since the buffer is the same as that shown in FIG.6, the operation control of the buffer can use the control programsshown in FIGS. 25A to 25C.

OTHERS Locking of Pallet in Stocker

In the above two embodiments and their various modifications, pallets phooked by the shelves 156 are simply supported at their flanges 38 bythe shelves 156 from the lower direction. For this reason, when thestocker 24 is vertically moved to feed a pallet p to the robot 12, thesupporting positions of the pallets p supported on the shelves 156 maybe shifted. If the supporting positions of the pallets p are shifted,the hooks 186 of the draw-out/draw-in mechanism 172 in the draw-out unitmay fail to engage with the first notches 38a of the pallet p supportedby the shelves 156 at the draw-out position. As shown in FIGS. 52 to 54,a lock mechanism 600 for locking the pallets p at their supportingpositions can be provided in the stocker 24, resulting in practicaladvantages. In order to effect the lock mechanism 600, as shown in FIG.52, an engaging hole 38d, locked by the lock mechanism 600, is formed inthe rear end portion (i.e., an opposite end portion with respect to theconveying direction d and in which the second notch 38b is formed) ofthe lower surface of each flange 38 of a pallet p.

As shown in FIGS. 53 and 54, the lock mechanism 600 comprises a lock rod602 attached to and extending vertically behind the elevating frame 152.The upper and lower ends of the lock rod 602 are disposed through guidemembers 604a and 604b attached at the upper and lower ends of the rearportion of the elevating frame 152 so as to be vertically reciprocal.

In order to vertically reciprocate the lock rod 602, an air cylinderC_(R) is fixed at the lower end of the rear portion of the elevatingframe 152 through an air cylinder mounting plate 606. The upper end of apiston 608 of the air cylinder C_(R) is connected to the lower end ofthe lock rod 602. When compressed air is not supplied to the aircylinder C_(R), the piston 608 is biased to the retracted position. Whencompressed air is supplied to the air cylinder C_(R), the piston 608 isbiased to the projecting position.

Lock members 610 are attached to the lock rod 602 (vertically moved asdescribed above) at the same pitch as the shelves 156 in correspondencewith pallets p. Each lock member 610 is constituted by a mounting piece610a fixed to the lock rod 602, and a lock pin 610b integrally formed onand projecting upward from the upper surface of the distal end of themounting piece 610a. The lock pin 610b is formed to be inserted in theengaging hole 38d formed in the lower surface of the rear end of eachflange 38 of the pallet p.

Each lock pin 610b is regulated at an unlock position separated andbelow each pallet p, as shown in FIGS. 53 and 54, while the air cylinderC_(R) biases the piston 608 to the retracted position. When the aircylinder C_(R) biases the piston 608 to the projecting position, eachlock pin 610b is regulated at a lock position at which the pin 610b isinserted in the corresponding engaging hole 38d of each pallet p fromthe lower direction.

The air cylinder C_(R) is arranged to be operated from the lock positionto the unlock position since supply of compressed air is stopped priorto the draw-out operation of a pallet p from the elevating frame 152 ofthe stocker 24 onto the draw-out base 168.

Since the lock mechanism 600 is arranged as described above, while theelevating frame 152 is vertically moved in the stocker 24, compressedair is kept supplied to the air cylinder C_(R) of the lock mechanism600. For this reason, each lock pin 610b of the lock mechanism 600 isinserted in the engaging hole 38d of each pallet p. As a result, all thepallets p are locked in a supported state on the shelves 156 by the lockmechanism 600.

Therefore, even if the elevating frame 152 is vertically moved, thesupporting positions of the pallets p are satisfactorily fixed by thelock mechanism 600. That is, when a pallet p is drawn out, it can bereliably engaged with the hooks.

When the elevating frame 152 is stopped to draw out the pallet p, supplyof compressed air to the air cylinder C_(R) is stopped. Each lock pin610b is disengaged from the corresponding engaging hole 38d, and eachpallet p is set to be slidable along the conveying direction d on theshelf 156.

In this manner, with the lock mechanism 600, shift in supportingposition due to the vertical movement of the elevating frame can beprevented. The hooks 186 of the draw-out/draw-in mechanism 172 in thedraw-out unit 154 can always be reliably engaged with the first notches38a of a pallet p supported on the shelf 156 at the draw-out position.

In the control operation of the stocker with the lock mechanism, thefollowing points need only be added. More specifically, when the targetshelf is moved to the draw-out position of the draw-out unit 154 in thestocker, if a pallet has a lid 40, the air cylinder C_(S2) (FIG. 16) foropening the lid is driven to open the lid, and the air cylinder C_(R) isdriven to disengage the lock pin 610b from the hole 38d. Thereafter, thedraw-out operation of the pallet to the draw-out unit 154 in step S82(FIG. 24A) is started.

The vertical movement of the elevating frame of the stocker is startedafter the air cylinder C_(S2) (FIG. 16) is returned to close the lid andthe air cylinder C_(R) is returned to set the lock pin 610b in the lockstate.

Parts Replenishment to FAC

The FAC system of the basic embodiments achieves an efficient feeding ofparts from the stocker to the robot and an efficient supply of partsfrom the buffer to the stocker. However, the FAC system cannot solelyperform parts feeding to the robot and parts supply to the stocker.Therefore, parts replenishment from an external unit to the FAC systemin a certain form is necessary. Parts supply to the FAC system includesan automatic replenishment by an unmanned vehicle and a productionmanagement computer, as well as manual replenishment. It cannot beuniquely determined which replenishment means is better for both meanshave different merits and demerits.

Cases for externally replenishing the FAC system with parts are:

1: a case wherein since a new pallet is fed to the stocker, a palletretaining the parts is used up although pallets retaining other partsstill remain; and

2: a case wherein empty pallets stacked on the unloading mechanism 76interfere with the vertical movement of the elevator.

When these two cases occur, they directly cause an interruption of therobot. Therefore, the pallets must be immediately replenished to thebuffer.

Another condition of replenishing pallets to the buffer is:

3: Each time an empty pallet is formed in the stocker, a palletretaining the corresponding parts is replenished using an unmannedvehicle. However, this requires frequent reciprocal operations of theunmanned vehicle between the FAC and the warehouse or cumbersome manualreplacement of empty pallets.

The robot detects the remaining parts count zero in step S36 or S30 inrobot control (FIG. 23A). Simultaneously with detection, a robot issuesa replenishment request for instructing the replenishment of a newpallet. The destination of the replenishment request is a centralproduction management computer for causing an unmanned vehicle toperform the replenishment as one mode. Another mode is a warning lampfor informing an operator of an empty pallet. The former mode isautomatic replenishment, and the latter mode is manual replenishment.

Replenishment of a new pallet to the buffer includes a buffer stopoperation for adding a new pallet to existing pallets on the bufferbase, and an operation for transferring an empty pallet stacked on theunloading mechanism 76 to the buffer. Therefore, a pallet replenishmentpreparation timing and a pallet replenishment timing to the buffer areimportant in terms of the efficient operation of the robot.

Replenishment by Unmanned Vehicle

New pallet replenishment by the unmanned vehicle will be describedhereinafter with reference to FIGS. 55A and 55B.

FIG. 55A schematically shows a pallet supply system including thecentral production management computer, the unmanned vehicle, and thelike. In step S770, the FAC sends the above-mentioned replenishmentrequest to the production management computer in the assemblingprocesses. If no replenishment preparation instruction is sent back fromthe production management computer, the flow advances from step S772 tostep S776 to check if unloading of an empty pallet by the unloadingmechanism 76 of the elevator in the FAC is started. If it is notstarted, the flow returns to step S770, and assembly is continued.

In step S750, the replenishment request from the robot is counted andrecorded. Since the production management computer grasps the productionmanagement schedule, even if parts in a pallet in one stocker are usedup, the same parts may be retained in other pallets on the buffer. Theproduction management computer recognizes and manages this fact.Therefore, if the replenishment request is sent from the robot,replenishment by the unmanned vehicle is not immediately performed inresponse to the request. Instead, in step S752, traced recorded dataassociated with pallets stacked on the buffer, which is stored in theproduction management computer, is checked in step S752. A vehicle startinstruction is issued to the unmanned vehicle as needed, in step S754.

When the replenishment request from the robot is received in step S750,the unmanned vehicle is not immediately started. However, the requestedpallet unloaded from the warehouse is stacked on the unmanned vehicle toprepare for the starting. Each time a pallet is stacked in the unmannedvehicle, the warehouse supplies data associated with the pallet (FIG.25A) to the unmanned vehicle.

Another factor in the predetermined condition in step S752 is thefollowing case. That is, parts in a pallet are used earlier than theproduction schedule, and empty pallets are stacked on the unloadingmechanism 76 which is enough to interfere with the vertical movement ofthe elevator earlier than the prediction of the production managementcomputer.

When the predetermined condition occurs, the vehicle start instructionis supplied to the unmanned vehicle in step S754, and in step S755 S756,the lapse of a predetermined period of time is monitored. Thepredetermined period of time is slightly shorter than the time requiredfor the unmanned vehicle to reach the FAC. After the lapse of this timeperiod, in step S758, a pallet replenishment preparation operation startinstruction is supplied to the FAC. If a plurality of FACs are equipped,the production management computer detects in advance times required formovement of the unmanned vehicle to the FACs. If the replenishmentpreparation at the FAC is completed slightly before the unmanned vehiclearrives at the FAC, replenishment from the unmanned vehicle can beimmediately started as soon as the unmanned vehicle arrives. Morespecifically, since the replenishment preparation is not performed inthe FAC for the predetermined period of time, assembly by the robot canbe continued, resulting in practical merits.

In step S762, the unmanned vehicle is traveling toward the FAC uponreception of the vehicle start instruction from the productionmanagement computer.

When the FAC system receives the replenishment preparation startinstruction from the production management computer in step S772, itstarts the preparation operation in step S774. FIG. 55B shows thepreparation operation in detail. If the FAC system itself detects thenecessity of replenishment preparation operation, the flow advances tostep S776 S778, and the preparation operation is started. Uponcompletion of the preparation operation, arrival of the unmanned vehicleis waited for in step S780. The standby time must be at a minimum forthe above-mentioned reason. When the unmanned vehicle has arrived,pallet replenishment from the unmanned vehicle to the buffer isperformed in step S782, and data associated with a new pallet isadditionally stored in the memory area shown in FIG. 25A.

The replenishment preparation operation will be described below withreference to FIG. 55B. FIG. 55B shows portions associated with palletreplenishment of control programs of the management microprocessor ofthe FAC system, the microprocessor of the elevator for controlling theunloading mechanism 76, and the microprocessor for controlling thebuffer.

When the management microprocessor receives the replenishmentpreparation instruction from the production management computer in stepS800, it stops the operation of the elevator and the like in step S802.In step S804, the management microprocessor supplies an upward movementstart instruction of the buffer base to the buffer. In step S806, themanagement microprocessor waits for the upward movement completionmessage from the buffer.

The buffer which has received the upward movement instruction in stepS840 moves the buffer base upward in step S842. After the buffer base ismoved upward, if a pallet which has already been separated at that timeis hooked on the separation pawls 68, the buffer releases hooking tostack the separated pallet. In step S846, the buffer causes theseparation pawls 68 to hook the lowermost pallet on the buffer base.After the pallet is hooked, if the buffer base is moved downward in stepS848, the pallet is hooked on the separation pawls 68, and no pallet ispresent on the buffer base. In step S850, the buffer sends the bufferpreparation completion message to the unloading mechanism 76.

Upon reception of this message in step S822, the unloading mechanism 76rotates the rollers in step S824 to start the transfer of an emptypallet towards the buffer. In step S826, the mechanism 76 sends amessage indicating this to the buffer. 20 When the buffer receives thismessage, the flow advances to step S852 step S854, and it waits forarrival of the unmanned vehicle. As described above, the unmannedvehicle must arrive soon after.

When the unmanned vehicle has arrived, the buffer transfers the emptypallets to the unmanned vehicle, and at the same time, receives newpallets therefrom by driving the corresponding rollers. In step S857,the buffer base is moved upward together with the new pallet to add thenew pallet to the existing pallets hooked on the separation pawls 68.The buffer receives data associated with the newly added pallet from theunmanned vehicle in step S858, and updates the memory content in stepS860 shown in FIG. 25A.

The replenishment preparation operation of a new pallet is performedimmediately before the unmanned vehicle arrives, so that the stop timeof the unmanned vehicle can be minimized.

Manual Replenishment

Manual pallet replenishment is summarized as follows. Upon everyreception of a replenishment request from the robot, the warning lamp isturned on. An operator who sees indication of the warming lamp manuallydischarges an empty pallet, stacks a new pallet, and inputs pallet dataat the I/O device 18.

FIG. 56A shows an input display screen on the I/O device 18, FIG. 56Bshows an arrangement of input keys, and FIG. 56C shows a generalreplenishment operation sequence. The input keys include a "palletreplenishment key" and a "preparation completion key", as shown in FIG.56B The replenishment operation will be briefly described with referenceto FIG. 56C.

When the replenishment request is input from the robot, the warning lampor the like is turned on in step S900. The operator who sees thisconfirms the requested pallet in step S902, and turns on the "palletreplenishment key" in step S904.

Thus, the buffer moves the buffer base to the replacement position (theposition of the separation pawls 68) in step S906 to hook the existingpallets on the pawls. The unloading mechanism 76 discharges emptypallets thereon in step S908.

At this time, the operator takes out the empty pallet in step S910, andplaces the requested pallet on the buffer base in step S912.

In step S916, the operator inputs the data as shown in FIG. 56A at theI/O device 18. Each time the data is input, the data shown in FIG. 25Ais updated in step S918, and the updated pallet order is displayed onthe CRT screen of the I/O device. The routine consisting of steps S916to S918 is repeated a number of times corresponding to the number ofrequired pallets.

In step S922, the operator turns on the "preparation completion key".

In this manner, the buffer calculates a stroke from the position of theseparation pawls 68 to the uppermost pallet placed on the buffer base instep S924, and starts the downward movement corresponding to thecalculated stroke in step S926, thus adding a new pallet to the existingpallets. Then, the FAC system restarts its operation.

As described above, the manual pallet replenishment operation iscompleted.

In the above two embodiments and thief various modifications (to bereferred to as the embodiments and the like), the elevator body 86 andthe elevating frame 152 which are vertically movable are slidablysupported at four corners, in other words, are slidable while beingsupported from two sides. However, the present invention is not limitedto this arrangement. For example, the elevator body 86 and the elevatingframe 152 may be slidably supported on a corresponding pair of columns,i.e., slidably supported in a cantilever manner.

In the above-mentioned embodiments and the like, a plurality of commonparts x are retained in one pallet p However the present invention isnot limited to this. For example, a plurality of types of parts x₁ andx₂ can be retained in one pallet p.

In the above-mentioned embodiments and the like, a plurality of palletsp are stacked on the buffer base 52 of the buffer 22. However, thepresent invention is not limited to this. For example, a plurality ofstanding pallets p may be held in a lateral direction.

In the above-mentioned embodiments and the like, when one of palletsstacked on the buffer base 52 is separated by the separation pawls, theseparation position is adjusted to absorb a manufacturing error, suchthat the positions of the separation pawls are fixed, and the bufferbase 52 is vertically moved. However, the present invention is notlimited to this. For example, the buffer base 52 may be fixed inposition, and the separation pawls may be vertically moved. When aplurality of pallets retaining the same type of parts are stacked on thebuffer, a previously stacked pallet (or an upper pallet) may beseparated first.

EFFECTS OF EMBODIMENTS

The above-mentioned embodiments can provide the following effects.

A: Effects obtained in the FAC system

The FAC 10 basically comprises the stocker 24 which stocks a pluralityof shelf-like pallets each retaining a plurality of parts x in a lateralplane, and performs vertical movement to extract the desired one ofthese pallets to a fixed draw-out position, and the robot 12 for takingout the parts x from the pallet drawn out to the draw-out position andassembling the parts into a product. For this reason, the robot 12 canquickly receive parts from the pallet p drawn out to the predetermineddraw-out position.

More specifically, in order to feed parts to the robot 12, the followingthree operations need only be performed: (1) a pallet p is drawn out tothe draw-out unit, and the robot performs a take-out operation of theparts in the draw-out unit; (2) the pallet is drawn into the stocker 24;and (3) the elevating frame of the stocker 24 is moved vertically untilthe stock position of a pallet retaining parts to be fed nextcorresponds to the draw-out position. In this manner, the assemblyoperation time required for assembling one part in the robot 12 can bereduced, and the assembling operation control can be simplified.

In article feeding apparatuses associated with Japanese PatentApplication Nos. 61-200949 and 61-200905 described in the prior art, thestocker is fixed in position, and the draw-out unit is verticallymovable. For this reason, in order to feed a pallet from the stocker tothe robot, the following five operations must be performed: (1) a palletp is drawn out to the draw-out unit; (2) the draw-out unit is movedvertically to a parts take-out position by the robot and at the partstake-out position, the draw-out unit is subjected to the parts take-outoperation by the robot; (3) the draw-out unit is moved vertically so asto be returned to the position at which the pallet was drawn out; (4)the pallet is drawn into the stocker 24; and (5) the draw-out unit ismoved vertically to the stock position of a pallet retaining parts to befed next.

Note that with the above arrangement, the parts can be efficiently fedfrom the stocker 24 to the robot 12.

A-1: Efficient Parts Feeding to Robot

A-1-1: Pallets p₁, p₂, and p₃ respectively having three differentthicknesses can be stocked in an arbitrary combination as long as thecapacity of the stocker 24 permits. In this manner, a pallet pcorresponding to the size of parts x can be selected. For example, aninefficient retaining state wherein only a layer of low-profile parts isstocked in a deep pallet, can be prevented.

The flanges 38 are integrally formed on the upper side edges of a palletp. The flanges 38 are provided to be hooked on the shelves in thestocker 24. However, the flanges 38 not only have this single function,but also have notches used for moving the pallet in the conveyingdirection d. Movement of the pallet p is executed in a mechanicallyengaged state by engaging the hooks with the notches. Therefore, thepallet movement can be reliably executed. In addition, its stop positioncan be accurately determined.

In particular, in the arrangement of the previous embodiment, the firstand second notches 38a and 38b and the corresponding hooks 108, 116, and126 are formed into an isosceles trapezoidal shape, so that they can becomplementarily engaged with each other. In this manner, even if theposition of the pallet p is slightly shifted, the hooks can be reliablyengaged with the notches. This engaged state is maintained such that theinclined surface of the trapezoidal hook abuts against that of thetrapezoidal notch. More specifically, in a state wherein the hooks areengaged with the notches, no gap is formed between the hooks and thenotches. In this manner, when the hooks are moved along the conveyingdirection d to convey the pallet, the movement of the hooks can bedirectly transmitted to the pallet, and the pallet can be smoothlyconveyed without receiving any shock.

A-1-2: Parts necessary for product assembly, the process order requiredfor the assembly, and selection of pallet p (shelf) for each process canbe arbitrarily selected and altered. For example, the parts can beretained in accordance with a process order starting from the uppermostpallet in the form of one pallet/one type of parts. For example, thesame type of parts x can be taken out from the same pallet p in aplurality of different processes. In this manner, factors associatedwith assembly can be flexibly set.

A-1-3: Since the process order can be set manually or automatically bythe host computer, a variety of process orders can be set in accordancewith the sizes of factories and the like. The process order can beconveniently altered in correspondence with the specifications of aproduct even in the field such as factory.

A-1-4: The robot manages the remaining parts count Z in each palletstocked in the stocker. Thus, a pallet replacement preparation operationstart timing and an empty pallet replacement operation start timing canbe managed by the robot itself. More specifically, since the robot asthe assembling body manages the operation start timings, it can selectoptimal start timings so as not to interfere with assembly.

A-2: Efficient Parts Supply

The basic arrangement also comprises the buffer 22 for supplying partsto the stocker 24 in addition to the stocker 24. When necessary parts xare supplied from the buffer 22 to the stocker 24, a pallet which hasfed the parts to the robot and become empty is drawn out and unloaded bythe stocker 24. A full pallet drawn out from the buffer is alternatelystocked at the empty stock position after the above-mentioned draw-outoperation. Thus, a state wherein the stocker 24 can always be filledwith parts can be realized.

In particular, necessity (remaining parts count=1) is predicted toreplace a given pallet p which will become empty since parts x retainedtherein will be used up soon. If it is determined that the replacementis necessary, a new pallet is prepared in place of the pallet which willbecome empty (replacement preparation), thus improving parts feedingefficiency.

The efficiency can be basically improved by the buffer 22 in which aplurality of supplementary pallets are prepared, and which selects andseparates a pallet p retaining the same type of parts as the parts xwhich are used up from these pallets. When the replacement preparationinstruction is sent to the buffer, the buffer selects and separates apallet p. In this manner, if the remaining parts count in the pallet pbecomes zero, the replacement preparation has been completed at thattime, and the replacement operation can be immediately performed. Thus,a total replacement time of the pallet p can be reduced, and the robot12 can be prevented from being stopped or if stopped, the stop time canbe minimized. The above effect is clarified by the following modes.

A-2-1: The following effect can be achieved in association with theseparation position of the buffer. That is,

A-2-1-1: When the separation position is fixed at a predeterminedposition, only a pallet p to be separated is separated at the separationposition. For this reason, after the pallet is separated, the separatedstate is recovered so that the remaining pallets can be set in a stackedstate again. Thereafter, a pallet at an arbitrary vertical position canbe separated.

Note that the separation position is set to be one of the following twotypes of predetermined positions. That is,

A-2-1-1-a: When the separation position is set at an arbitrary verticalposition above the buffer base 52, an arbitrary pallet is selected andseparated from pallets p stacked on the buffer base 52.

Since each of the pallets stacked on the buffer base 52 has amanufacturing error, the height of a pallet to be separated at theseparation position cannot be accurately defined. For this reason, inthis embodiment, since the sensor 80 for accurately defining theseparation position is arranged, even if the manufacturing errors areaccumulated, a desired pallet p can be reliably separated.

A-2-1-1-b: When the separation position is defined to separate a palletdirectly placed on the buffer base 52, pallets p are stacked on thebuffer base 52 in the generation order of the replacement requests inthe stocker 24, from the lower position. With this arrangement, as willbe described later, the buffer 22 itself can comprise the replacementfunction, and the elevator 26 can be omitted.

A-2-1-2: When the separation position is set for all the pallets pstacked on the buffer base 52, all the pallets are simultaneouslyseparated upon the separation operation. In this manner, an arbitrarypallet can be drawn out and replaced with an empty pallet, thussimplifying the replacement operation.

A-2-2: When the replacement preparation operation is performed betweenthe buffer 22 having the separation function of A-2 and the stocker 24,the pallet separation position in the buffer 22 must match with theshelf position of an empty pallet in the stocker 24. The matching modesare as follows.

A-2-2-1: When the stocker 24 has the movement (vertical movement)function and the separation position of a pallet p is fixed in buffer22, the stocker 24 is moved to a position adjacent to the separationposition so that the separation position in the buffer 22 matches withthe shelf position of an empty pallet p' in the stocker 24. Since thestocker 24 itself is moved to receive the full pallet, the replacementtime of an empty pallet can be shortened.

A-2-2-2: The replacement preparation operation can be performed in acombination of the buffer 22 having the separation function described inA-2, and the elevator 26 which is reciprocally moved between theseparation position of the buffer 22 and the replacement position of thestocker 24 to convey the separated pallet to the stocker 24. In thiscase, as described in A-2-2-1, since the stocker 24 itself is not movedto receive the full pallet, the-draw-out operation of a pallet to therobot 12 in the stocker 24 can be prevented from being interrupted.

A-2-3: The same effect as described above can be obtained by combiningthe buffer 22 having the separation function described in A-2, thetransfer 550 having a replacement function that the transfer is fixed inthe separation position to be adjacent to the buffer 22, and the stocker24 which is vertically moved to a position adjacent to the transfer 550.

A-2-4: When identification data associated with the pallets stacked onthe buffer base are stored in the memory, a supply operation from thebuffer to the stocker can be easily and reliably performed. That is, theorder of necessity of the new pallets from the buffer is not related tothe stacking order of pallets on the buffer base. Therefore, when thepallets are replenished to the buffer base, identification data ofindividual pallets to be replenished need only be supplied to thebuffer, and the stacking order of the pallets to be replenished need notbe taken into consideration. As a result, the stacking order of palletsto be replaced in the unmanned warehouse, manual stacking order ofpallets to be replenished onto the buffer base, and the like need not betaken into consideration, resulting in an efficient operation.

In contrast to this, without the memory data, if the full pallets arestacked on the buffer base in the known generation order of emptypallets, no problem occurs.

A-3: Efficient Replacement Operation of Empty and Full Pallets

After the replacement preparation operation is performed, the actualreplacement operation of an empty pallet p' and a new pallet p isperformed, thus achieving an efficient replacement operation. In orderto execute the replacement operation, the following three modes can beemployed.

A-3-1: The above-mentioned effect can be achieved by the arrangementcomprising the stocker 24, the vertically movable elevator 26, and thebuffer 22 having the separation function of pallets p stacked in anarbitrary order, the elevator 26 comprising the replacing mechanism 96.

A-3-2: The above-mentioned effect can be achieved by the arrangementcomprising the stocker 24, the buffer 22 having the separation functionof separating, at a fixed separation position, pallets p stacked in anarbitrary order, and the transfer 550 arranged adjacent to the fixedseparation position, the transfer 550 comprising the replacing mechanism96.

A-3-3: The above-mentioned effect can be achieved by the arrangementcomprising the stocker 24, and the buffer 22 for separating, at a fixedseparation position, pallets p stacked in a predetermined take-outorder, the buffer 22 comprising the replacing mechanism 480.

A-3-4: The replacing mechanism 96 is arranged to move pallets p in astate wherein the mechanism 96 is mechanically engaged with the notches38a and 38b of a pallet p using the hooks 108, 116, and 126. In thismanner, in the replacement operation, the pallet p can be reliablymoved, and its stop position can be accurately defined. Thus, thereplacement operation can be reliably executed.

There are two modes according to the number of hooks. That is,

A-3-4-1: In the arrangement comprising the three types of hooks, i.e.,the first hooks 108 which are engaged with the first notches 38a of apallet p to take out the pallet p from the buffer 22, the second hooks116 which are engaged with the second notches 38b of the pallet p topush out the pallet p to the stocker 24, and the third hooks 126 fordrawing in an empty pallet p' from the stocker 24, the third hooks 126are positioned immediately below the second hooks 116 to be movedtogether. Thus, the movement stroke of the first hooks 108 is set to beequal to that of the second hooks 116. As a result, the arrangement ofthe replacing mechanism 96 can be simplified and the replacementoperation control can be facilitated.

As a hook drive source, the following two modes are employed. That is,

A-3-4-1-a: The three types of hooks are mounted on the common slideplate 106, and the slide plate 106 is reciprocally driven by a singledrive motor, so that the three types of hooks are driven by a singledrive source, thus achieving simple control.

A-3-4-1-b: The two types of hooks as the first and second hooks 108 and116 are reciprocally driven by a first drive motor, and the third hooks126 are reciprocally driven by a second drive motor. With thisarrangement, the number of drive motors is increased as compared to thecase of A-3-4-1-a. However, the arrangement for driving the hooks can besimplified.

A-3-4-2: In the arrangement comprising the two types of hooks, i.e., thefirst hooks 108 which are engaged with the first notches 38a of a palletp to take out the pallet p from the buffer 22 and second hooks 116 whichare engaged with the second notches 38b of the pallet tp to push out thepallet p toward the stocker 24, the replacing mechanism 96 can properlyfunction. In this case, since the second hooks 116 must perform twodifferent operations, the operation time is prolonged as compared to thecase of A-3-4-1. However, a simple, inexpensive arrangement can bemanufactured.

A-4: Efficient Unloading Operation of Empty Pallet

When the replacement operation is executed such that an empty pallet p'is drawn out from the stocker 24 and a full pallet p is pushed into thecorresponding position, the empty pallet p' is produced in the FACsystem 10. In this embodiment, since the unloading mechanism 76 for theempty pallet p' is arranged, a predetermined number or less of emptypallets p' can be satisfactorily unloaded. As a result, the emptypallets p' can be prevented from being stacked in a predetermined numberor more to interfere with the next replacement operation.

During the unloading operation, when the empty pallet p' is stacked onthe unloading mechanism, the following various modes can be employed.

A-4-1: The elevator body 86 of the elevator 26 is moved downward to aposition immediately above the unloading mechanism 76 or immediatelyabove empty pallets p' already stacked on the unloading mechanism 76, soas to stack an empty pallet p' held below the elevator body 86 onto theunloading mechanism 76. With this arrangement, empty pallets p' can bestacked in principle on the unloading mechanism 76 without interferingwith the replacement operation of the pallets.

A-4-2: The unloading mechanism 76 comprises the lift mechanism 402, andthe lift mechanism 402 is moved upward to stack an empty pallet p' heldon the replacing mechanism 96 onto the unloading mechanism 76. Ascompared to the case of A-4-1, the possibility of interfering with thereplacement operation can be reduced.

Note that in the arrangement comprising the lift mechanism 402, thefollowing two modes can be employed.

A-4-2-1: When the lift mechanism 402 is arranged below the elevator body86, the lift mechanism 402 is moved upward to a predetermined positionand can wait at that position until an empty pallet p' is drawn in theelevator body 86. The downward movement time of the elevator body 86 canbe shortened. In this manner, the time required for unloading the emptypallet p' can be reduced, so that the next replacement operation can beprevented from being delayed.

A-4-2-2: When the lift mechanism 402 is not arranged below the elevatorbody 86, the following two modes can be employed. That is,

A-4-2-2-a: When the lift mechanism 402 is arranged below the transfer550 provided at a fixed position to be adjacent to the separationposition of the buffer 22, the transfer body 552 of the transfer 550 onwhich a drawn empty pallet p' is held is fixed in position. Thus, inorder to stack the empty pallet p' on the unloading mechanism 76, thelift mechanism 402 is a necessary component.

A-4-2-2-b: In a state wherein the buffer 22 comprises the replacementfunction, when the lift mechanism 402 is arranged below the buffer base52, the buffer base 52 on which the drawn empty pallet p' is held isfixed in position. Therefore, in order to stack the empty pallet p' onthe unloading mechanism 76, the lift mechanism 402 is a necessarycomponent.

A-4-3: As described in A-4-2, when the lift mechanism 402 is arranged,the sensors S₁, S₂, and S₃ are arranged, so that the following twoeffects can be achieved. That is,

A-4-3-1: When the sensors S₁, S₂, and S₃ are used to define the upwardmovement position of the lift mechanism 402, the upward movementposition changes depending on the height of empty pallets p' stacked onthe lift mechanism 402. More specifically, if the predetermined upwardmovement position is defined to allow stacking of pallets p₃ having amaximum thickness regardless of the height of the pallets p', whenpallets p₁ having a minimum height are stacked, a considerably large gapis formed between the bottom surface of the pallet p₁ having the minimumheight and the uppermost position of the lift mechanism 402 or thepallets stacked thereon. For this reason, if an empty pallet p₁ ' is tobe stacked through this gap, the position of the empty pallet p' isshifted, and cannot be satisfactorily stacked.

However, since the sensors S₁, S₂, and S₃ can define the optimal upwardmovement position in accordance with the height of each pallet, theabove-mentioned problem will not occur, and the empty pallet p' can bereliably stacked on the lift mechanism 402.

A-4-3-2: When the sensors S₁, S₂, and S₃ are used to define the upwardmovement position of the lift mechanism 402 and the lift mechanism 402is arranged below the elevator body 86, the sensors S₁, S₂, and S₃define the upward movement position of the lift mechanism 402 so that anempty pallet p' is received at the lowermost position of the elevatorbody 86. Thus, the downward movement time of the elevator body 86necessary for transferring the empty pallet p' from the elevator body 86to the unloading mechanism 76 can be minimized. In this manner, the timenecessary for transferring the empty pallet p' to the unloadingmechanism 76 can be shortened, and the possibility of delaying the nextreplacement operation can be reduced.

A-5: Effect Obtained by Capping Lid 40 on Pallet

In order to take out parts x retained in a pallet, when a pallet p withan open upper surface is used to convey the parts x, a lid 40 isprovided to each pallet p in order to protect the retained parts frombeing contaminated with dust or the like during conveyance or in a stockstate in the buffer 22 and the stocker 24. The lid 40 closes the openupper surface while, at the same time, is capable of being opened. Sincethe lid 40 is attached to each pallet p, the parts x retained in thepallet can be reliably prevented from being contaminated with dust orthe like.

A-5-1: The lid 40 covers the pallet p for the total period excluding aninterval for which the pallet p is brought to the draw-out position tothe robot 12 in the stocker 24. A period for which the upper surface ofthe pallet p is "open" is limited to a draw-out period as an open periodnecessary for taking out parts x therefrom. Thus, entrance of dust orthe like into the pallet p can be minimized, and the parts x can beprevented from being contaminated with dust or the like as much aspossible.

A-5-2: When the lid 40 is removed from the pallet p, the lift-up arm 160in the lid opening mechanism 170 is linearly moved obliquely upward fromoblique lower direction, and engages with the side edge of the lid 40through the corresponding third notch 38c of the pallet p from the lowerdirection, thereby lifting up the lid 40. The linear movement of thelift-up arm 160 allows for the use of a single drive source therefor. Inaddition, the lift-up operation time can be shortened, and cost can bereduced.

Note that the lift-up arm 160 passing through the corresponding thirdnotch 38c of the pallet p is arranged so as not to interfere withmovement of the pallet p in the conveying direction d while it lifts upthe lid 40.

A-6: Locking of Pallet in Stocker

In the stocker 24, each pallet p is supported on the corresponding shelf156 of the vertically movable elevating frame 152. In a state whereinthe pallet p is supported on the shelf 156, the movement of the pallet pin the conveying direction is locked by the lock mechanism 600. In thismanner, even if each pallet p receives a moving force along theconveying direction due to vibration caused by vertical movement of theelevating frame, since it is locked by the lock mechanism 600, thepallet p can be reliably locked at a predetermined position on the shelf156.

As a result, in a state wherein the elevating frame 152 is stopped andlocked by the lock mechanism 600 is released, each pallet p is alwaysbrought to a predetermined position. The pallet draw-out operation tothe robot and the draw-in operation of an empty pallet can be reliablyexecuted.

B: Effect of Easy Process Alteration

The effects of the embodiment of the FAC described above are thosemainly concerning hardware and a control program for controlling thehardware when the robot, stocker, elevator, buffer, lift mechanism, andthe like are variously combined. Since software such as a controlprogram must have a feature of easy alteration, effects in terms ofalteration flexibility of the control program used in this FAC will bediscussed below.

In the embodiments, parts used in a given process are related using avariable G as a process. A pallet and a shelf position for stocking thepallet are related using a variable S, and the shelf position variablesS are arrayed (S G!) based on the processes G. In this manner, therelationship of processes .increment.→ shelf positions .increment.→pallets .increment.→ parts is clarified. Therefore, if this array ischanged, the processes are reordered, and if the processes arereordered, the shelf positions stocking the pallets need not be changed.In addition, the control program need not be altered.

Since the array is displayed on the CRT screen of the I/O device, theprocesses and the like can be easily altered.

C: Effect of Efficient Replenishment from External Equipment to FAC

In this FAC system, the parts feeding operation from the stocker to therobot at a fixed position and the parts supply operation from the bufferto the stocker are fundamental operations. The supply operation isperformed in units of pallets. Therefore, if parts are used up in theFAC system, a new pallet filled with parts must be replenished fromexternal equipment.

In this FAC system, the parts feeding process and the parts supplyprocess by means of pallets are independently performed. Since these twoprocesses are independently performed, parts feeding from the stocker tothe robot is not immediately stopped even if the parts supply to thestocker is disabled. Parts replenishment is divided into a preparationprocess in the FAC (including a process for hooking all the existingpallets on the buffer base at upper positions, and a process forunloading empty pallets stacked below the elevator), and an actualreplenishment process in which the FAC and external equipment (unmannedvehicle) for feeding parts to the FAC are cooperated. Thus, the partssupply process coincides with the preparation process of the palletreplenishment. Therefore, the total time of parts replenishment can beshortened, and as a result, a stop time of the unmanned vehicle can bereduced. In manual replenishment, although it is cumbersome, dataassociated with pallets on the buffer base, the number of which isincreased since new pallets are replenished, can be easily updated inaddition to the effect described in B.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A method for feeding articles to a robot from a stocker retaining plural kinds of containers, each container containing a predetermined kind of articles, said method comprising the steps of:temporarily storing a stack of containers each retaining a predetermined kind of articles in a temporary storer including a vertically moveable table on which the containers are stacked and a separator for separating one container from the others; memorizing information of a stacking position of each container stacked on the moveable table; sending an article request command for requested articles to the stocker in accordance with a pre-programmed feeding order to select a container stocked in the stocker containing the requested articles; feeding articles from the selected container in the stocker to the robot while detecting any containers in the stocker which are about to be emptied; sending, when a container is detected to be emptied, a container separation request to the temporary storer to separate a full container containing the same kind of articles that are about to be emptied from the container from other containers in the temporary storer using the separator on the basis of memorized information of the stocking position of the containers on the moveable table; and replacing only the container detected to be emptied in the stocker with the full container from the temporary storer while articles are being supplied from another container in the stocker to the robot.
 2. A method for feeding articles to a robot as set forth in claim 1, further comprising the step of disposing the containers in a stacked relationship on the table so that they can be supplied to the stocker one-by-one from a bottom-most container in the stack.
 3. A method for feeding articles to a robot as set forth in claim 1, further comprising the step of engaging an empty container in the stocker and removing it therefrom.
 4. A method for feeding articles to a robot as set forth in claim 3, further comprising the steps of:supporting the containers independently in the stocker on a frame having a plurality of shelves; and vertically moving the frame from a position in which an uppermost shelf opposes the separator and a position in which the lowermost shelf opposes the separator.
 5. A method for feeding articles to a robot, comprising the steps of:temporarily storing a stack of containers, each retaining a predetermined kind of article, in a temporary storer including a vertically moveable table on which the containers are stacked, and a separator for separating one container from the others; memorizing information of a stacking position of each of the containers stacked on the moveable table; feeding articles from a selected one of a plurality of containers stocked in a stocker to the robot; separating a designated container full of articles from other containers in the temporary storer when a container in the stocker is emptied by vertically moving the table and making the separator engage the designated container, as articles are being fed to the robot from other containers in the stocker, wherein said separating step takes place based on memorized information of the stacking position of the designated container; removing the designated container from the temporary storer; replacing the empty container in the stocker with the designated container; restoring the remaining containers in the temporary storer into a stacked condition by disengaging the separator and moving the table; and updating the information of the stacking positions of the remaining containers on the table in response to the removal of the designated container.
 6. A method for feeding articles to a robot as set forth in claim 5, further comprising the steps of:discharging the empty container from the stocker. 